Washington served two four-year terms and then left office, setting a precedent that eventually became law. The next two presidents, John Adams and Thomas Jefferson, represented two schools of thought on the role of government. This divergence led to the formation of the first political parties in the Western world. The Federalists, led by Adams and Alexander Hamilton, Washington's secretary of the Treasury, generally represented trade and manufacturing interests. They feared anarchy and believed in a strong central government that could set national economic policies and maintain order. They had the most support in the North. Republicans, led by Jefferson, generally represented agricultural interests. They opposed a strong central government and believed in states' rights and the self-sufficiency of farmers. They had the most support in the South.

For about 20 years, the young nation was able to thrive in relative peace. Its policy was to be friendly and impartial to all other nations. However, it was not immune from political developments in Europe, particularly in Britain and France, which were at war. The British navy seized American ships headed to France, and the French navy seized American ships headed to Britain. Various diplomatic negotiations averted hostilities during the 1790s and early 1800s, but it seemed only a matter of time before the United States would have to defend its interests.

War with Britain came in 1812. Fighting took place mostly in the Northeastern states and along the east coast. One British expeditionary force reached the new capital of Washington, in the District of Columbia. It set fire to the executive mansion — causing President James Madison to flee — and left the city in flames. But the U.S. army and navy won enough decisive battles to claim victory. After two and a half years of fighting, and with a treasury depleted by a separate war with France, Britain signed a peace treaty with the United States. The U.S. victory ended once and for all any British hopes of reestablishing influence south of the Canadian border.

By the time the War of 1812 ended, many of the serious difficulties faced by the new American republic had disappeared. National union under the Constitution brought a balance between liberty and order. A low national debt and a continent awaiting exploration presented the prospect of peace, prosperity, and social progress. The most significant event in foreign policy was a pronouncement by President James Monroe expressing U.S. solidarity with the newly independent nations of Central and South America. The Monroe Doctrine warned against any further attempts by Europe to colonize Latin America. Many of the new nations, in turn, expressed their political affinity with the United States by basing their constitutions on the North American model.

The United States doubled in size with the purchase of the Louisiana Territory from France in 1803 and Florida from Spain in 1819. From 1816 to 1821, six new states were created. Between 1812 and 1852, the population tripled. The young nation's size and diversity defied easy generalization. It also invited contradiction.

The United States was a country of both civilized cities built on commerce and industry, and primitive frontiers where the rule of law was often ignored. It was a society that loved freedom but permitted slavery. The Constitution held all these different parts together. The strains, however, were growing.