When Thomas Jefferson completed his second term as president in March 1809, he was succeeded by his friend and ally James Madison. Madison was the principal author of the Constitution; coauthor of The Federalist Papers, which ensured its ratification; and secretary of state in Jefferson’s administration. Like Jefferson, he sought to end foreign interference in American affairs and to resolve conflicts between Indians and white residents on the nation’s frontier. Congress itself was divided over how best to address these problems. By 1815 the United States had weathered a series of domestic and foreign crises, including another war with Britain, but American sovereignty remained fragile. At the same time, even though Madison (like Jefferson) believed in a national government with limited powers, he found himself expanding federal authority.