In the winter of 1944–45, as his health began to fail, and as the maelstrom of events typical of a world trapped in a brutal and destructive war swirled around him, President Franklin D. Roosevelt struggled to keep the grand alliance between the United States, Great Britain and the Soviet Union intact. Only if he succeeded in this, Roosevelt believed, would the post-World War II era prove to be one of peace rather than conflict. During this period of great international importance, two critical factors hindered FDR's pursuit of global peace: first, his close-knit group of advisers had been whittled away by ill health and internal arguments; and second, the complex set of emotions that had developed within the wartime alliance between the US, Britain and the Soviet Union were becoming increasingly poisonous. Eventually, the strain became too much; Roosevelt died in April 1945, and under a new President, Harry S. Truman, the post-World War II era descended into acrimony and Cold War as the emotional tide that FDR had kept in check overwhelmed everything in its path. This deceptively simple, yet crucial, argument is at the heart of Frank Costigliola's new book.

For the last twenty years, Costigliola has been building up to this moment with a series of path-breaking articles examining the emotional basis of the collapse of the grand alliance and the onset of the Cold War. One of the most vital aspects of this approach is that it treats policymakers and politicians as human beings, affected by life's vicissitudes and eventualities just like everyone else. Ill health, grief, and emotional ties between like-minded individuals, and the consequences of person-to-person interaction, all influence the course of history. In one sense, of course, this is a patently obvious thing to say; how could these factors not influence someone's perspectives and behaviour? On the other hand, however, proving this and demonstrating its importance are remarkably difficult things to do, and require careful reading of a huge array of sources no less than a clear conception of the importance of language in understanding the course of history. It is to Costigliola's great credit, then, that he succeeds admirably in making a persuasive case for the importance of emotion in first creating the grand alliance and then, later, bringing about its downfall.

Broadly speaking, his reinterpretation of this period has two key parts. The first concerns the creation of the alliance, and the interaction between Roosevelt, Winston Churchill and Joseph Stalin – not to mention numerous high-level advisers in each country – which brought about a relationship forged more out of necessity than out of ideological kinship. Central to this development, Costigliola argues, were the personal links that underpinned the diplomatic process. Churchill's bond with his daughter-in-law, for example, was vital in helping to create the Anglo-American alliance due to her numerous sexual relationships with prominent American officials like Averell Harriman, Ed Murrow, Henry Luce, William Paley and Jock Whitney, as well as the staunch friendship that she developed with Harry Hopkins, FDR's close adviser and regular point of contact between Washington and London. The intimacy generated by Pamela Churchill's relationships – which she in all likelihood shared unreservedly with her father-in-law – helped to bring British and US officials closer together. Such personal alliances, Costigliola makes clear, provided the framework for the military and political alliance that soon followed. The very nature of Stalin's Russia, of course, made an identical situation in UK–US–Soviet relations unlikely; there were similarities, though, and the social side of the diplomatic process between London, Washington and Moscow was, arguably, as important as the political and military arguments. Close relationships were formed between US officials working out of their embassy and elite Russian women, while the nature of Soviet society compelled British and American officials to come together regularly to discuss their views of the war. Moreover, the epic drinking sessions and parties that typically accompanied any diplomatic dealings with the Kremlin created an environment in which closeness and respect were equated to one's capacity to last the pace. The alliance against Hitler had numerous political and strategic aspects to it, then, but it was built on a foundation of wide-ranging emotional ties.

More tellingly still, the second key aspect of the book's argument concerns the way that these emotional bonds began to fray as the war progressed. If the intense pressure of war had helped to bring the allies closer together, so the enormous tensions and strains that it subsequently threw up ultimately worked to drive them apart as entrenched ideological differences could no longer be kept beneath the surface. Even then, Costigliola argues, the Cold War was in no way preordained or inevitable: Roosevelt, had he lived, could have ensured that widespread tension did not develop into outright hostility. Hence, though he comes across as a significantly flawed personality, FDR is central to the book's events. Once he died, the dam holding back the tide of emotional anger – evident, perhaps most viscerally, among George Kennan and Averell Harriman, whose views of life in Stalin's Russia had become increasingly bitter – fell away and a new President, less experienced and more receptive to the counsel of experienced officials like Kennan and Harriman, adopted a firmer stance toward the Soviet Union. Again, strategic, military and political factors all clearly played a role here – and, indeed, had continued to do so throughout the wartime era. But the very essence of the relationships that emerged in mid- to late 1945, shaped as they were by rancour and mistrust, came about due to the emotional threads of the great alliance. Disappointment and hurt feelings, to put it another way, were as prevalent as the incompatibility of capitalism and Stalinism.

For all its success in challenging readers to think afresh about a period on which so much has been written, there are still a couple of points that warrant being mentioned here. The first, perhaps unfairly, is in relation to the question of sources. On both the British and the American sides, Roosevelt's Lost Alliances is powerfully supported by reference to a host of sources culled from a wide range of archives, published sources and memoirs. The same is not true, however, on the Soviet side. This is, of course, for good reason, as Stalin's Soviet Union was not the sort of place where writing one's thoughts in a diary or expressing great emotion about ongoing events was to be recommended. Nonetheless, this does mean that the evidence provided on the Russian side of the story, while no less captivating than that provided elsewhere in the book, is somewhat less compelling.

Second, there is the issue at the very heart of the book's thesis: the question whether or not a surviving Roosevelt could in fact have avoided the descent into Cold War that occurred after 1945. To be sure, Costigliola provides much evidence to support this claim. It is FDR, after all, who is vital to holding his own inner circle of advisers and the London–Washington–Moscow relationship together for the majority of World War II. Furthermore, Roosevelt was abundantly aware that future peace depended upon a solution being implemented once the war was over that was acceptable to all the interested parties. At the same time, though, it is also clear that his capacity to keep doing this was diminishing rapidly by 1944 as ill health took its toll on the President and his close circle of advisers. By the time that he began his fourth term in 1944, in fact, his health was in the midst of a swift decline. Consequently, I am not sure that the counterfactual argument is wholly persuasive. Would FDR, given his declining health, really have been capable of maintaining international peace between increasingly disputatious allies? Like all intriguing counterfactual arguments, we can never truly know the answer. Nevertheless, a line of enquiry involving a surviving Roosevelt suggests a range of other counterfactual arguments that could have exerted at least as much influence on the international situation in the 1940s. What if Churchill's stroke in 1941 had been more serious? Would a new leadership in Downing Street have pursued the war in the same manner? What if Stalin had died during the war? Would a replacement leader in the Kremlin have been amenable to continued cooperation with the West? Either of these eventualities, one might argue, could have shifted the emotional balance of the alliance as much as FDR's death.

Such questions, of course, are part and parcel of what happens when writing a book as analytically sophisticated as this one. By compelling us to view the momentous events of the 1940s in a new way, Roosevelt's Lost Alliances performs a critical service for the field of international history and opens up a number of avenues for new research. That it does so in a field as saturated as this one, moreover, highlights the remarkable level of innovation that Costigliola has brought to the subject and, as all good history should, it makes us think in new and profound ways about how differently the course of history could have played out.