This chapter examines the compound republic established by the U.S. Constitution, emphasizing its innovative balance of national and state powers. Unlike the Articles of Confederation’s league of states, the Constitution was ratified by the people, not state legislatures, and thereby creates a national government with direct authority over individuals, but only within its assigned sphere. This “new science of politics,” as Hamilton termed it, departs from Montesquieu’s view that republics suit only small territories, enabling a robust union capable of addressing external threats and internal defects such as the ineffective taxation and defense under the Articles. Madison’s writings in The Federalist highlight the Constitution’s blend of national and federal elements, ensuring legitimacy through popular sovereignty while preserving state autonomy in areas outside the enumerated powers. The chapter explores the Webster-Hayne Debate and Jackson’s response to South Carolina’s tariff nullification to refute secession and nullification and reaffirm the Constitution’s supremacy, while acknowledging states’ roles in “interposition,” as in the 1798 Virginia and Kentucky Resolutions, to alert citizens to potential federal overreach.