Debates about war powers often center on who can start or enter wars, and understandably so given the stakes. But that focus obscures the many other constitutional authorities that determine whether, when, how, and why the United States fights – and whether it prevails. As American warfare and security strategies evolved – often in ways the Framers could not have foreseen – so too did the interlocking system of war powers that governed those strategies.
All democracies grapple with some basic questions about war powers, but the United States stands apart. No other democracy’s constitution has governed a similar rise from military infant to giant amid such seismic changes in the nature of war and theories of security. The United States has fought a great many conflicts along the way to its present status as a global superpower, and it has done so on the basis of relevant constitutional text that has remained largely unchanged since 1787. The Constitution functioned when the United States had almost no standing army and when it was a superpower; when America eschewed alliances and when it led them; in big wars of survival and almost countless small conflicts of choice; and in periods when American foreign policy emphasized geographic isolation or expansion, neutrality or hegemony, military restraint or interventionism. The Constitution’s time-tested versatility in adapting to strategic contexts, and its general – if far from perfect – capacity across those diverse circumstances to reconcile military necessity with democratic accountability helps explain why it remains the world’s oldest, still-active written constitution.
This judgment of the Constitution’s effectiveness is not meant to deny defects or to glorify past constitutional practice and strategic decision-making. Nor is it meant to suggest that their ultimate effects have all been for the good. Constitutional evolution helped the nation win the wars it most needed to, but the American war-powers system contributed to grave foreign policy blunders, tragic losses abroad, and dark moments for civil liberties at home. Reasonable minds may disagree whether the United States became a global superpower because of the Constitution or in spite of it. It is hard to dispute, though, that prevailing constitutional interpretations and practices evolved over time in ways that generally supported a broad array of strategies for addressing varied security imperatives, and – so far – without succumbing to tyranny as a result.
This concluding chapter draws together many strands of this story to highlight neglected ways the Constitution has shaped – and will continue to shape – armed conflict and American strategy. It closes by explaining how that history unsettles familiar frames, points to practical reforms, and offers a perspective on rapidly unfolding events today.
War Powers, Revisited
Constitutional war powers have marched in continually shifting formations – more so than scholars often acknowledge. To mention just a few progressions: Over time, decisions to make war came to turn on the exercise of other congressional and executive war powers that alter the conditions leading up to those decisions. Some strict interpretations of constitutional powers, especially those governing who wages war and how they do so, proved unworkable as American foreign policy and forms of warfare changed, and so all three branches arrived at more flexible interpretations. Growing American military strength expanded and dramatically transformed the President’s powers over where U.S. forces fight and Congress’s powers to prepare and mobilize for war. Constitutional powers to end war and to prevent its recurrence work differently today than they did at the Founding, because the United States now fights or seeks to deter different kinds of wars and for different reasons.
These powers do not operate independently or sequentially; they function as an interconnected system whose components continually interact. Preparations for war, for example, affect whether and how wars erupt, the types of war that are fought, and the chances of ultimately achieving that war’s objectives. How, where, and why wars are waged affects how and when they are ended, which in turn affects how the next war might begin or be averted, and so on. Constitutional powers to decide these questions currently operate in ways the Constitution’s architects would scarcely recognize. None of those powers is held exclusively by one branch.
If this sounds complex, that is the point: War and American approaches to it have been complex, and so therefore have frameworks for governing them. Meanwhile, if some of the war-powers arrangements discussed below seem obvious, that is another key point: Many constitutional shifts and adaptations that were once hotly contested are now so settled that they are barely noticeable anymore. The controversies that begot them are also long forgotten.
Powers for Making War – Or Averting It
Some parts of this book’s story are well known. With regard to starting or entering war, the President’s power to use force has, in practice, expanded over time. Although many scholars peg that expansion to the Korean War – still the largest war launched by the President without express congressional approval – this book aligns with those who observe that the expansion was gradual, starting in the early republic.
Setting aside the issue of when this trend began, scholars and political leaders have continued a never-ending argument over whether expanded presidential power increases the risk of costly wars. As this book shows, that question is too simplistic. Wars usually result from or are averted by a series of moves and decisions by both political branches. Each branch exercises a wide range of constitutional powers, all while adversaries engage in their own moves and countermoves. To meaningfully analyze how the Constitution governs making war, the starting point should not be when Congress declares or authorizes it or when the President orders forces into battle. No doubt those decision points are important, but they are consequences of prior moves by the political branches, each exercising auxiliary powers.1
Presidents have long exercised powers that can materially sway the chances of war – either by raising those chances or by lowering them. Presidents threaten war. They reassure allies in public and private. They mobilize existing military forces, or they move them into harm’s way. As the standing U.S. military has grown – and especially since the dawn of the Cold War, when its expansion became permanent – presidents have stationed forces strategically around the world. The reverse is also true. Presidents stand down from threats, remove forces from dangerous situations, and withdraw diplomatic assurances. Historically, factions in Congress sometimes questioned whether such moves usurped their power, but today, the President’s constitutional powers to do many of these things are seldom questioned.
As American grand strategy changed, some presidential powers took on new importance. For example, when the United States was still a fragile, militarily weak nation, the President’s power to threaten war was of modest consequence, because America’s policy was to hide behind geographic buffers and avoid entanglement in foreign disputes. After World War II, when the President and Congress together made deterrence of rivals and reassurance of allies central to American foreign policy, the constitutional power to threaten war became more policy-significant than the power to wage it. During the Cold War, presidents’ nuclear threats – backed by forward deployments and public commitments – often mattered more than actual force. Presidential powers to posture American military capabilities likely helped avert wars, without thereby activating constitutional processes for entering them. Were the United States to retreat from underwriting its allies’ security and some aspects of the global order, as some political leaders on both the right and the left are now calling for, the importance of powers to threaten war might recede.
The Executive Branch most visibly wields the powers that can raise or lower the risk of war, but those authorities are not exclusively the President’s. Congress, too, shapes what Alexander Hamilton called the “antecedent state of things.” The legislature can authorize limited force short of armed conflict, as it did in the republic’s first low-level “Quasi-War” against its erstwhile ally France. It can limit where U.S. forces may operate, as it did when authorizing a draft in 1940. Congress can pass resolutions expressing American will to take military action. It took such action weeks before the Cuban Missile Crisis, perhaps the most dangerous moment in world history. It can reinforce American defense commitments, as it recently did by passing laws restricting the President’s authority to withdraw from NATO or to reduce U.S. troop levels from some allied territory.2 There may be constitutional limits to many of these legislative actions – which affect the President’s freedom of action and send signals to foreign audiences – especially when Congress’s moves bump up against the President’s commander-in-chief powers. Those limits have been debated since the earliest days of the republic. Yet Congress holds many levers to influence the context in which military force may be used downstream.
Even if Congress holds exclusive power to make war, as many critics of presidential unilateralism maintain, some of the most basic ways that Congress exercises that power are now so widely accepted that we forget their constitutionality was once disputed. Take the issue not of whether Congress exercises its declare-war power, but how it does so. It is often assumed that because Congress has not declared war since World War II, authorizing force has become the constitutional equivalent. But they are not the same. Whereas a war declaration formally places the nation in a state of war, congressional force resolutions often give the President vast discretion over when to use force and whether to use it at all. Through much of early American history, delegating to the President such broad discretion over the use force was constitutionally uncertain and contested. Today, by contrast, even open-ended force resolutions are usually sufficient to satisfy those who argue that only Congress may take the nation to war.
Congress has had potent strategic reasons, as well as political ones, to enact broad or open-ended force resolutions of the type that might not have passed constitutional muster in earlier eras. Sometimes Congress used broad resolutions to back planned operations; at other times, it saw them as tools for deterrence, rapid response, or diplomatic pressure. Had this constitutional issue resolved differently – had Congress concluded, as many members argued, that it lacked constitutional authority to delegate to the President the choice of whether to go to war – Congress would probably not have approved as many conflicts, but the President might have bypassed the legislature more often. The matters of whether and how Congress approves war are interdependent.
Alongside these visible forms of military commitment, a quieter set of instruments has emerged, as the Executive Branch and Congress together negotiated a separate set of constitutional practices for making covert war. Practices designed for overt conflict, like explicit force authorizations, fit poorly with covert paramilitary operations, which rely on stealth and deniability. This constitutional track was mostly laid at a time when the Executive resorted to covert war to avoid costlier and riskier overt war – a strategic option enabled by Congress’s and the Executive’s joint Cold War enterprise of creating a permanent agency charged with conducting clandestine activities. Yet stealthy and deniable warfare is harder to check. So, over time, the elected branches negotiated special congressional oversight arrangements. Although the statutory framework is now well established, the constitutional bases and limits of covert warfare are – like the conduct of such operations – still murky.
Powers over Who Fights America’s Wars
Debates over the President’s power to start wars overshadow the history of interbranch cooperation regarding who fights those wars. With its control of the purse strings and its special powers to build and support armed forces, only Congress could grow the military from small units to a powerful war machine. But those congressional powers swelled over time, extending well beyond straightforward choices about expanding or shrinking the ranks and arsenal. Those powers have been vitally important to whether, where, and how the United States wages war – and how it prepares for future war.
In some cases, the elected branches jointly recruited or mobilized Americans in radically new ways to fight the nation’s wars. The issue of assembling and maintaining armed forces was so sensitive at the Founding that the Constitution’s text contains more detail on that issue than almost any other. But the drafters could not predict the new types of wars, new military capabilities, and new strategies for using military means that have emerged over the nation’s history. Congress enabled different types of wars by creating different types of military forces.
The Framers might have been startled that by the mid-nineteenth century, for example, the United States would be capable of waging a major war of territorial expansion across North America. Many would have been alarmed that, to wage that war, Congress and the President bypassed the militia system and instead raised an expeditionary army composed largely of wartime Volunteers inducted directly into the national Army. Only in World War I did all three branches finally accept the constitutionality of a national draft, allowing the United States to wage total war overseas. Earlier chapters showed that each of those policies for filling military ranks turned on contested interpretations of vague constitutional text. Each of them expanded national war powers at the expense of the states. And they were adopted by Congress and the Executive together in pursuit of a new American security strategy in which both branches had a say. In other words, flexible interpretations facilitated strategic pivots that rigid readings would have delayed or blocked. Today, there may be few constitutional limits on how the national government might fill military ranks – so long as Congress and the Executive Branch together deem such measures necessary to meet military challenges of the day.
At critical moments in history, the elected branches have not only expanded the size of the armed forces but have also radically reorganized the structure of American armed forces to prepare for or wage new types of wars. In so doing, Congress and the President together also reset more of the Constitution’s original balances.
At the twentieth century’s turn, for example, federal legislation revamped state militias into standardized Army reserve forces and created a more efficient general staff capable of planning for major war. Opponents of those reforms viewed eighteenth-century constitutional features like state autonomy and siloed administration as vital checks against militarism, while advocates dismissed those features as outdated burdens that obstructed military modernization in a tense geopolitical environment. After World War II, Congress and the Executive consolidated the Army, Navy, and nascent Air Force within a single Defense Department, so that the United States could better project its ascendant global influence. In doing so, Congress placed in the President’s hands large forces that were always kept ready for his use. Both of these overhauls were made by the elected branches in tandem and in peacetime, to prepare for – and they hoped to prevent – the next war. These exercises of war powers through constitutional processes facilitated – some critics would argue propelled – strategies of military primacy and activism.3
The government is once again grappling with what it means to extend these authorities beyond the traditional boundaries of conflict. Congress and the Executive have acted jointly in recent years to build special military forces and organizations for defending and waging war in cyberspace and outer space. Political leaders recognize that the geography of war is no longer just physical or terrestrial, especially when American military capabilities are so reliant on digital networks and space-based assets. Much as past congresses worked with the Executive to remake U.S. armed forces for the nation’s emergent role as a great power and then as a superpower, today’s Congress is now slowly doing so for war in the ether – amid rapid technological change and commercially driven military innovation. A constitutional system that its designers intended to curb needless American bloodshed is currently being adapted to cyber- and space “combat” that, in the most optimistic predictions, may be relatively bloodless. War powers that were once flexed for publicly visible American power-projection across continents are currently being geared for digital battlegrounds of invisible ones and zeros.
Powers of How and Where to Wage War
Beyond the polarizing question of how the United States goes to war, and the quite-settled matter of Congress’s flexible powers to build and structure armed forces for doing so, some of the most far-reaching issues concern the powers to wage wars once begun. The scope of the President’s commander-in-chief powers has been contentious since the Founding. So too has the scope of Congress’s ability to restrict those powers, which the President and lawmakers have battled over from the nation’s first international conflict through its recent ones. Meantime, some government activities for waging war that were once at the center of war-powers debates, like strong federal control of the economy, are no longer even seen as war-powers issues at all. Those activities remain essential to war – but for the last century, they have become routine functions of the administrative state.
The President, acting through his subordinates, has always exercised authority to direct military operations in the field. President Washington was already exercising such power on the Western frontier at the republic’s birth. However, the conceptual boundaries of “military operations” became blurrier – and more overlapping with Congress’s powers to legislate the means for waging war – as American warfare changed. In the Mexican–American War, the President argued that law-of-war rules on occupation empowered, indeed required, the Commander in Chief to temporarily govern captured territory and its inhabitants. In the Civil War, both branches cast emancipation of enslaved people as an operational necessity. In World War II and the Korean War, the President argued that the entire national industrial base was a modern battlefield, and that he therefore had broad managerial and regulatory powers. During the Global War on Terror – in which intelligence about terrorist networks and plots was key – some Bush Administration officials treated fiber-optic Internet cables and covert interrogation rooms as conflict theaters. Across these episodes, control of the war effort implicated domestic governance as profoundly as it did foreign affairs.
Over time, constitutional practice has tended to accommodate strategies that expand the scope of the “battlefield” – especially when the Congress and the Executive work in concert. In this area, courts rarely draw clear boundaries, and edge cases are instead negotiated by the elected branches in ways that leave constitutional issues undecided. Advances in artificial intelligence (AI) are enabling military systems, including lethal ones, to operate with increasing autonomy, and the Executive has worked internally and internationally to establish guardrails. Were Congress to step in – for example, by restricting the missions or targets for which autonomous weapons may be used – there are no clear or stable answers as to how far it could constitutionally go.4 If history is a guide, the Executive and Congress would probably arrive at some bargain that left constitutional lines unsettled.
Closely tied to the President’s command of how forces wage war is his command of where they wage it. Constitutional scholars tend to focus much more on the former, but the latter has been at least as consequential. Congress seldom legislates tight territorial limits around warmaking authority. This congressional forbearance often facilitates the use of American military might by providing the President with wider options and denying the enemy the possibility of a safe haven beyond defined boundaries. As a result, American military growth over time converted a once-modest presidential power to direct geographically confined operations into a sweeping power to set war aims and lead global alliances.
In the early republic, the Army and Navy’s small size naturally limited the President’s discretion. With Congress’s approval, the President could send naval forces to combat French privateers in the Caribbean or engage North African corsairs in the Mediterranean, but he lacked the military resources to expand those conflicts much further. American military growth gave the President much wider discretion as to where to wage war. In 1846, President Polk maneuvered the United States into a war by moving troops into a border zone. War with Mexico then became a war in Mexico and then a war for Mexico – because the President decided so and sent large forces there. Four decades later, the “splendid little war” with Spain in Cuba became a long, secondary war for the Philippines – because of executive war plans and operational improvization, using the modern Navy that Congress had earlier chosen to provide and maintain. Congress may have declared war in 1846 and 1898, but the President converted them into entirely different kinds of wars through actions they commanded on land and at sea.
When the United States became a military giant, its wars expanded geographically, too – and the President’s power to decide where to wage them assumed even greater significance. As William Rehnquist, then heading the Office of Legal Counsel, explained when advising President Nixon on operations in Cambodia, World War II had required “military decisions on a global scale,” as well as choices “that partook as much of political strategy as they did of military strategy.” Should the United States, for example, concentrate its resources on the Atlantic or Pacific front, or fight simultaneously on both? Where should the recapture of allied territories in Europe and Africa begin? Such judgments, he noted, were made by the allied chief executives and commanders – without any formal congressional role on the U.S. side.5 In line with this logic, Nixon extended the Vietnam War across its neighbors’ borders. Congress eventually responded, in a rare act of geographic constraint, by limiting which national boundaries the President could cross and how force could be used. More recently, the President and lawmakers have occasionally tussled over whether the President’s constitutional and statutory authority to use force in Iraq includes some authority to take action against targets in Iran and other neighboring countries. In this constitutional space, military means and political judgment – far more than legislative text – have usually defined the territorial limits of American war.
As a superpower, the United States has grappled with constitutional questions about the regional or global scope of war powers from which other democracies have largely been spared. Today, the President’s practical authority to widen the geography of conflict spans cyberspace and outer space – borderless arenas where U.S. capabilities dominate – because Congress has organized, funded, and sustained specialized military forces to operate there.
Undoubtedly, the President’s powers to command forces swelled over time. But he still operated under the shadow of congressional power. Sometimes Congress exercised sway by statute, but more often it did so with oversight tools like hearings, political suasion, and proposed legislation.
Moreover, Congress’s powers for waging war grew over time, too – especially those related to mobilizing the home front. At the Founding, the fear of potential wartime expansions of Congress’s domestic powers (such as to tax) was in many eyes a prime reason to check government impulses toward war. Lincoln asserted emancipation powers during the Civil War as a military measure, but the Civil War Congress had also enacted laws authorizing Union forces to liberate categories of enslaved persons. Around the same time, Congress also permanently revamped the U.S. financial system in ways that would probably have been unconstitutional but for the fact that they were war measures. Once warfare consumed entire nations in World War I, the Necessary and Proper Clause became the basis for legislatively converting a loosely regulated economic system to a centrally managed statist one geared for military victory. In these periods, congressional war measures remodeled American government and society, including the federal government’s relationship to the states.
The Civil War and World War I marked the largest swings between Congress’s wartime constitutional powers and its peacetime constitutional powers. That differential has narrowed considerably over the last century, not because Congress’s wartime powers have waned, but because its peacetime powers have ballooned since the New Deal. The twentieth-century advent of nuclear weapons arguably raised war’s external, foreign-relations stakes far beyond anything imaginable to the Founding generation. But when it comes to internal governance, the stakes of making war – and therefore the significance of which branch does so – declined overall during the past century.
Powers Over War Ends and Ending Wars
Debates on constitutional war powers often focus on who decides whether to fight, while neglecting which branch determines why war is waged. Those questions may sound the same, but they are not. The range of possible aims has grown as U.S. global interests and responsibilities have grown. Beyond the battlefield, concepts of “victory” became more open to debate. Yet studies of war powers often give little attention to the issue of who controls war aims. Whose theory of victory matters? The Constitution’s architects likely never anticipated the sheer range of war outcomes made possible by America’s military growth, making the constitutional power to set and revise war aims more consequential than they imagined.
One might have expected that clear goals would be worked out through the process by which the President proposes and Congress enacts a war declaration or authorization. Time and again, though, the United States has gone to war without interbranch agreement on aims or end states. Even when Congress states a goal in its force authorization, it often does so only in very general terms, like preventing aggression or protecting U.S. security interests.
To be fair, most legislation involves ambiguous compromises. Wars are also fluid and unfold in unpredictable ways. Goals change. Showing one’s hand early can be a bad bargaining strategy. But in war, more than in other policy arenas, the President wields vast power to set and reset aims – especially as he commands the forces and conducts wartime diplomacy. Means and ends in warfare are closely tied – that is the essence of strategy – and the stakes over who controls war aims are enormous, especially because those aims can largely determine the war’s duration. The net costs of America’s quickest major ground war – the 1991 Iraq war – or one of its longest – the 2003 Iraq war – might have been very different had the first President Bush chosen to overthrow Saddam Hussein’s government or had the second President Bush not done so.
Yet Congress wields wartime influence over war ends, too. In the Mexican–American War, for example, Polk directed military operations to make the capture of Mexican territory a fait accompli, but he had to mind Congress’s views on territorial gains – because the President needed Congress’s money. In the Civil War, Radical Republicans in Congress wielded some powers over the means of war – specifically, confiscation of the enslaved people held by Confederates – to press an ultimate war goal of abolishing slavery. At the end of World War I, the Senate rejected the President’s ambitions of an international peace charter; Wilson had to watch the United States opt out of his own postwar diplomatic order. Congress at first propelled the President to defend South Vietnam and its neighbors, and later hastened the process of withdrawing U.S. forces from the region, knowing that communist forces would likely overrun Vietnam. The President may have a jumpstart on Congress and a stronger position, but war aims have repeatedly emerged through uneasy but consequential interbranch participation – each branch exercising a range of respective war powers as conflicts unfold.
That shared assortment of powers to set war aims is closely tied to powers to end wars. In general, the Constitution has provided a versatile framework for concluding wars, and processes for doing so have varied depending on the type of conflict and Congress’s political will.
Formally declared wars in the Founding era customarily closed with a peace treaty. Constitutionally, this meant that the Senate would have to approve war-ending agreements. That pattern worked for major state-on-state wars until World War I, when the Senate rejected the President’s treaty, and Congress and the President wrangled over how to un-declare war. The stakes of which branch turns off wartime constitutional powers were high because those powers on the home front were at that time so expansive. When the United States stopped formally declaring wars after World War II, the elected branches worked out other approaches for terminating wars and winding down wartime powers – including combinations of unilateral presidential actions and congressional resolutions, repeals, funding measures, legislation, or political pressure – sometimes with clear endpoints, sometimes not.
On one hand, the Framers would have been pleased that the Constitution contains many levers for ending wars. They wanted it to be easier to make peace than to make war – and not just for fostering international harmony but for containing government power at home. On the other hand, none of these levers is actually easy to pull. By creating large-scale standing forces after World War II, Congress made it simpler for the President to make war and harder for the lawmakers to end it. For their part, courts have been reluctant to judicialize the restoration of peace. The United States is now two-and-a-half decades into a “forever war” against terrorist threats and with no clear political consensus on what victory looks like. And yet, the gravity of this constitutional issue has ebbed and flowed over time, reflecting shifts in other constitutional powers. As noted earlier, the divide between wartime and peacetime powers on the home front was at its widest during World War I. The gap closed since then, much less because the powers provided by the wartime Constitution shrank than because the powers of the peacetime Constitution grew. But that divide could widen again in future conflicts, thereby making the constitutional process of ending war far more consequential than it has been in recent decades.
War Powers for International Governance
After World War II, the United States effectively turned from the traditional practice of ending wars through Senate-approved peace treaties to ending them though armistices, political agreements, and UN-sponsored settlements. At the same time, America became a principal architect and guarantor of collective security pacts aimed at preventing future conflicts. This marked a profound shift for a nation that had historically been wary of peacetime alliances. No other democracy’s constitution has governed such a role. It is remarkable that the American Constitution did not bend more than it did in providing power to preserve collective security, considering how much it bent for so many other strategic imperatives.
American political leaders in both elected branches have insisted on the Constitution’s primacy over any international pact. In practice, that commitment has meant relying on familiar constitutional formulas to determine when the President may use force to honor treaty pledges. Collective-security arrangements that depended uniquely on American military predominance – and thus raised distinctive constitutional-governance challenges for the United States – expanded, by degrees, the President’s already considerable authority to use force. But they did not push it into entirely new terrain. One fleeting constitutional innovation in 1945 would have allowed the President, with Congress’s blessing, to provide the UN Security Council with a standby U.S. force. Such a move would have shocked those Framers who opposed both peacetime pacts and standing armies. But the Cold War’s onset effectively mooted the idea, anyway, as superpower rivalry prevented the Security Council from deploying any force of its own, let alone a U.S. standby one. By contrast, as the book’s opening pages explain, one of the postwar era’s most consequential precedents involved presidential authority to base U.S. forces in potential flashpoints abroad, bolstering the credibility of collective security arrangements. Contrary to common expectations about presidential unilateralism, that power enabled and entrenched a strategy that may have reduced the risk of catastrophic wars.
At present, some American political leaders are calling into question postwar strategic orthodoxies and global military engagement. Pulling the United States back from its role in sustaining the alliance system would increase the practical significance of who, constitutionally speaking, controls going to war. Retreating from the role of security guarantor would make U.S. military action more selective, less automatic. A more restrained policy might, therefore, in theory, leave more room for joint, case-by-case decision-making between Congress and the President. But that restraint might also erode existing deterrents to war, leading to a proliferation of conflicts that could draw the United States in.
The Constitution and Future Warfare
It is hard to know how war powers will function down the line and what new questions will arise. The trajectory of warfare and security threats is hard to anticipate. As Lawrence Freedman puts it in his wonderfully titled The Future of War: A History, “There is no longer a dominant model for future war, but instead a blurred concept and a range of speculative possibilities.”6 American political leaders are now also challenging long-standing strategic doctrines built on security guarantees and other international commitments. There is no telling whether and where a new foreign policy consensus will settle.
Any coming security paradigm will to some degree rely on light-footprint American warfare, from air power and special forces to cyber-operations and unmanned systems. That approach is not a new phenomenon, though the technology on which it relies continues to evolve rapidly. Presidents have typically sought Congress’s approval for ground wars that threaten heavy U.S. losses, while they have justified unilateral light-footprint actions by emphasizing the reduced risk to American personnel. Modern executive-branch legal theories treat minimal expected American bloodshed as a factor supporting broad presidential power. But the very kinds of operations for which presidents claim they do not need congressional authorization – small-scale, low-visibility, limited-casualty ones – are also the operations least likely to trigger public scrutiny or political checks. In similar ways, the opaque workings of cyber-operations and AI-driven military decision-making will be difficult for Congress to oversee.7 Modern war powers sometimes operate in an accountability vacuum – where both formal legal checks and political constraints are at their weakest.8
Continued reliance on remote or stealthy means of warfare is just one part of the future, however, and a generation after the Cold War ended, the real possibility of great power war is back.9 Russia’s 2022 full-scale invasion to conquer Ukraine set off the largest European war since World War II – the type of conflict that risked spilling across borders and drawing in the United States with its own forces, not just through arms sales and intelligence sharing. How, constitutionally, the United States might enter such a great-power war is no doubt an important question. But so are constitutional questions of how the United States might prepare for, deter, provoke, wage, expand, contract, and end major wars of the future.
Take, for example, a possible war with China, which the Pentagon now openly calls its “pacing threat.”10 After two decades of counterterrorism operations and counterinsurgency warfare centered on the Middle East, the American defense establishment is heavily focused on preparing for a possible war with a peer rival. One set of scenarios involves what defense experts now call “hybrid warfare” or “gray zone conflict”: a blend of limited conventional conflict and skirmishing by unconventional means like cyber-attacks, disinformation campaigns, support for proxy forces, and economic subversion. There would be no marked distinction between soldiers and civilians, no lines dividing military and non-military means, and no bounded theaters of battle. In such conflicts, existing constitutional frameworks governing the start of wars will be of limited use – because there will be no clear start. Indeed, a reason that a foe might resort to these methods is to blur the crossover from peace to conflict.11
Should a hot war against China erupt, the war’s scope and intensity could exceed those of the twentieth-century World Wars. A Chinese assault on Taiwan or Chinese clashes with U.S. treaty allies around the South China Sea, for example, could ignite a full-scale conflict with the United States. That would raise a host of old war-powers questions alongside others that the nation has never faced.
Consider how such a war might play out compared to the past conflicts explored throughout this book. A presidential intervention to defend Taiwan, for instance, could well be regarded as constitutionally dubious, given that the scale of such a conflict could surpass even the Korean War – the only prior major ground war for which the President did not obtain express congressional authorization. A Chinese attack on one or more formal U.S. treaty allies in the region – Japan, South Korea, the Philippines, and others – would raise similar constitutional questions. But any advance legal assessment risks oversimplifying the complexities of such scenarios. Conflicts unfold through a series of actions and reactions. Steps and counter-steps, in turn, affect the constitutionality of what comes next.
In the unlikely event that China preemptively strikes U.S. forces in the region, the President would unquestionably have the power to respond with military force. But if China were to move gradually – perhaps from gray-zone actions by unofficial proxies, to occupying tiny Taiwan-administered islands, before next blockading Taiwan – the President would have to make decisions and legal assessments amid a fog of uncertainty as to China’s intentions. The President might temporarily deploy naval forces in the Taiwan Strait – or might withdraw them. The President might order military exercises nearby – or might cancel them. The President might issue redlines – or might back away from them. These actions fall squarely within the President’s established powers, and any of them might affect the likelihood of war or limit Congress’s freedom of action. The fast pace of events, coupled with the risk of rapid escalation (perhaps greater with military AI-systems involved), would also compress the decision-making space for U.S. political leaders and military commanders.
The President might make many of these decisions alone, but Congress has some agency, too. Congress has for decades drawn on its own constitutional powers to establish a policy of arming Taiwan, declaring any Chinese attack against it to be a threat to American security interests, and preparing plans for defending it against attack.12 The legislature has set, allocated, and overseen defense spending with special attention to a possible war with China, including by placing bets on certain types of military technologies. Congress has not, in any legal sense, authorized force. But it has helped set the stage for any potential conflict in ways that go beyond shaping American politics to prioritize defending Taiwan or projecting American power in the Pacific region. A future U.S. war over Taiwan would come not just from an eleventh-hour presidential decision, or even a set of presidential military and diplomatic moves, but also from legislative moves and pressures well before any crisis develops.
If tensions with China heat up, the President could seek Congress’s pre-approval for a war through a standing force authorization, but doing so might stoke the very war that the President is aiming to deter. American political leaders could instead bide their time before passing and signing a force resolution, but that would risk not having time to do so before a military crisis erupts. The President could use force at a crisis’s outset and seek Congress’s blessing soon after the fact, but one might judge that two-step move as constitutionally suspect. Especially given the increasing speed with which modern militaries can or must move, getting the constitutional sequencing right is very hard – going to Congress not too early, not too late – which is one reason why original powers to make war have bent in so many ways.
Some key constitutional aspects of a possible Sino–U.S. conflict concern not how war begins but how it is waged – and how the United States prepares to wage it. Effective future warfighting will require major shifts in how the nation arms and readies itself, with greater reliance on software-driven innovation and less reliance on costly legacy hardware.13 As in earlier eras of military transformation, modernizing defense acquisition and planning would demand sustained congressional-executive cooperation, especially Congress’s use of its Article I peacetime powers to build war capacity, to overcome entrenched resistance and remake the military–private sector relationship.
Beyond preparedness lies the nature of the conflict itself. Any major war with China would likely unfold on multiple fronts – from cyberattacks on communications networks and online propaganda campaigns to the real possibility of the first use of nuclear weapons against another nuclear-armed state. Instead of a sharp, decisive conflict, nuclear arsenals and mutual abilities to disable offensive systems could yield a grinding stalemate. The American public might face prolonged hardship on the home front of a kind not seen since the Civil War. Unlike in World Wars I and II, when the United States had months or years to scale up production and manpower, it would need to mobilize instantly an economy that is now both substantially de-industrialized and deeply intertwined with China’s.14 Such a war – against an adversary adept at managing its economy and controlling information – would be waged not only around the globe but also in cyberspace, across outer space, and through globalized supply chains, using forces and legal authorities Congress has provided for operating in those domains.
Many key war-powers questions relevant to such a conflict are settled, but others are not. In a prolonged war with China, maintaining supplies of key technologies and resources – like munitions, advanced chips, and critical minerals – could revive debates over how far the President may act without explicit statutory authority in twenty-first–century wartime. Efforts to counter enemy disinformation and surveillance – perhaps by disabling privately owned, online communication platforms harnessed for propaganda or intelligence – might prompt the Executive to override statutory limits or test the still-uncertain bounds of the First Amendment in wartime. Those dilemmas would be only magnified by the ubiquity and speed of today’s social media.
Regardless of Congress’s involvement at the start, the conflict’s duration, aims, and endgame would be heavily dictated by the President’s decisions. But many outcomes would require joint action. A protracted war would require returning to Congress (perhaps repeatedly) for funding. A decisive American victory would shatter the UN system and remake regional security alignments, requiring Senate or congressional action to forge new pacts. And then there is a possible outcome that has been rare in America’s largest wars: the United States could lose. The President might then have to work with Congress to implement a settlement and navigate a changed world order.
Reimagining the War-Powers System
Taken together, this history yields five lessons for understanding and reimagining the American system of war powers.
First, this book has demonstrated that the power to initiate hostilities cannot be understood apart from the larger and ever-shifting constellation of war powers. Decisions to begin wars have always been inseparable from powers to organize forces, set objectives, define the terms of peace, and others.
The chapters throughout the book show that wars rarely begin with a single moment or command. They arise – or are avoided – through a sequence of political and constitutional maneuvers. Although presidential action often captures the greatest public attention, the choices that enable or restrain conflict typically arise from sustained interaction between Congress and the Executive, including the creation and organization of the armed forces in the first place. Once war begins, presidents wield immense operational authority, yet Congress’s tools – appropriations, investigations, statutory limits, and political pressure – continue to influence how wars are fought and how they end. This overlapping of different war powers and constitutional actors extends to the timeline of war itself. Across eras, from the Quasi-War to Iraq, these patterns reveal that constitutional powers and practices – like strategy – cannot be neatly separated or analyzed in distinct and isolated periods of prewar, wartime, and postwar.
Second, this account has offered a corrective to familiar narratives of the “imperial presidency.” That common story overstates the growth of executive war powers in some ways – especially in relation to Congress’s war powers – and understates that growth in other ways.
The President’s ability to send forces into conflict has clearly expanded since the Founding, but so have other presidential powers that steer whether, why, how, and how long the nation fights – some evident only in studying wars that never came. Congress’s authority has expanded, too, with regard to raising and structuring armed forces, mobilizing the economy, and signaling commitments to allies. Much of this growth has flowed from the Necessary and Proper Clause, often paired with the power to create military forces, and much of it has come at the expense of the states.
Critics are right that today’s presidency wields immense military power – much more than the Framers intended. Yet the most consequential shifts in war powers have usually stemmed from joint decisions by Congress and the Executive to meet strategic demands, not just unilateral grabs or passive acquiescence. And, many of the most far-reaching shifts occurred not in war, but in peace.
Third, this account has underscored the limits of originalism for understanding or evaluating the exercise of war powers. Even in the early republic, the Constitution offered little concrete guidance as the nation’s military capacity and strategy evolved. Some gaps in meaning were filled through early practice, but many later conflicts and security imperatives forced political leaders to craft new practices and constitutional accommodations the drafters never envisioned. Each adaptation generated new questions, prompting further innovation as new strategic realities emerged.
Because the various elements of war powers are so tightly interconnected, restoring any one of them to its original position would reverberate through others – or else demand major changes in American defense and foreign policy. If, for example, the Declare War Clause were read, as the drafters likely intended, to require explicit congressional approval to defend an ally, Congress might be pressured to pass advance or open-ended force authorizations, or presidents might rely more on tripwire forces stationed where allies are most vulnerable to attack. But early chapters showed that many Framers would have balked at those alternatives as well. If the Militia Clauses were read strictly, as many Framers did, to confine federal use of state National Guard units to American soil, Congress might once again confront the need for a national draft – a constitutionally unsettled option in the early republic. Originalist fidelity is defensible in theory, but achieving it would entail far more legal and strategic upheaval than is often recognized.
Fourth, this study has shown that constitutional law sometimes steers strategy in ways that neither domestic nor international politics alone fully explain. If originalism fails to capture that strategic imperatives have over time reshaped – and must reshape – constitutional war powers, on the flip side, it is also a mistake to think that “law” in this area is all just politics and necessity.
In a general sense, it is no surprise that law in this realm has generally molded around strategic imperatives. National defense was an animating purpose behind the Constitutional Convention in the first place, and no interpretation that severely hamstrings the government’s capacity for national defense will stick. What work, then, is constitutional law actually doing here? If changes in American warfare and strategy reshape law, then aren’t war powers ultimately just politics and military expediency all the way down?
The episodes traced throughout this book reveal how constitutional law and process have not merely followed strategy but have shaped it – enabling, sustaining, and restraining it in turn. Across history, strategy has bent the Constitution, yet the Constitution has also sometimes bent strategy. At various moments, for example, constitutional practice propelled expansion, narrowed the President’s military options, and entrenched collective security commitments. More broadly, constitutional reasoning and processes have continually framed the politics of war. From the beginning, leaders have used the Constitution’s language and machinery to chart the nation’s course in war and peace.
Finally, experience across two centuries cautions against reductive claims about how best to curb presidential war-making – and points instead to more promising ways to strengthen the overall functioning of war powers. Since the Founding, debates have often been cast in binary terms, above all over whether constraining the President’s authority to use force makes war more or less likely. At present, growing distrust of executive power and wariness in many quarters about U.S. overseas intervention or commitments have revived calls for tighter legal restraints through rigid rules: narrowly limiting the threats that justify force, for example, or imposing automatic funding cutoffs under the 1973 War Powers Resolution.15
There is surely room to improve the system. But history shows that the effects of tightening or loosening any single authority – like the President’s ability to use force – depend on the wider constellation of war powers and the strategic context. The Framers learned this lesson early through practical experience, and real-world events have repeatedly confounded neat theories and exposed the limits of tidy legal formulas.
To say that no abstract, optimal solution exists is not to discount other interpretive considerations, like constitutional text, precedent, or the principle that no one person should hold unchecked powers of war and peace. Nor is it an argument against vigorous checks. Instead, it is a caution to evaluate the policy merits of any constitutional formula in light of evolving American strategy – recognizing that safeguarding national security is itself a core constitutional purpose. That is why this book has focused on how particular interpretations and practices have supported or hindered the strategies of their time, rather than searching for timelessly optimal arrangements.
Looking back, early American strategies of territorial defense paired naturally with tight limits on presidential force, narrow congressional delegations, and shared state-federal control of the militia. Later, strategies of expansion aligned with more flexible congressional powers to raise armies and broader presidential claims of self-defense. In the era of total war, powers of mobilization and neutrality-management overshadowed the formal authority to declare war. During the Cold War, deterrence and collective security depended on overlapping authority with presidential tilt to posture large forces and to make threats credible. In the twenty-first century, congressional involvement may not have prevented or shortened some costly interventions, but oversight and judicial review helped make the long war against terrorists more legally disciplined and operationally sustainable. As American grand strategy continues to oscillate between engagement and restraint over the long term, the balance of war powers between the branches will shift accordingly.
Put another way, evaluating the policy merits of any interpretation or proposed reform requires recognizing that constitutional law is never strategy-neutral. Strategic imperatives continually reshape constitutional practice, and locking in any fixed allocation of war powers inevitably constrains future strategic choice. From the Founding onward, calls for legal rigidity have often aimed precisely at imposing such strategic constraints – a reminder that claims of constitutional fixity are themselves strategic acts.
If strategy is about aligning means and ends, then viewing war powers as an interconnected system points to a more constructive reform path than recurring efforts to police any single decision point. Congress could strengthen its role through more frequent defense reviews, rigorous auditing of national-security strategy, and sustained scrutiny during budget and authorization cycles. These steps would bolster Congress’s ability to shape policy before crises erupt – and guide not only whether and how force is used but whether events become wars at all – rather than concentrating its leverage primarily at the moment of authorizing hostilities. Rebalancing war powers around oversight and strategic guidance, rather than rigid prohibitions, would reinforce constitutional checks while preserving the flexibility demanded by a rapidly changing geopolitical and technological landscape.
Looking ahead, if the United States continues underwriting a global order, war-powers debates will center on sustaining deterrence and managing regional threats. If the nation instead retrenches or pursues a more coercive form of military primacy, Congress’s role in authorizing force may take on added weight – especially if reckless adventurism comes to be seen as more dangerous than under-commitment. Either way, America’s course will depend on how both elected branches wield their war powers – from long before wars begin to long after they end.
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