The United States has operated under a two-party system for most of its history. For elective offices at most levels, state-administered primary elections choose the major party nominees for subsequent general elections. Since the general election of 1856, the major parties have been the Democratic Party, founded in 1824, and the Republican Party, founded in 1854. Since the Civil War, only one third-party presidential candidate—former president Theodore Roosevelt, running as a Progressive in 1912—has won as much as 20% of the popular vote. The president and vice president are elected by the Electoral College.
At first effectively neutral during World War II, the United States began supplying materiel to the Allies in March 1941 through the Lend-Lease program. On December 7, 1941, the Empire of Japan launched a surprise attack on Pearl Harbor, prompting the United States to join the Allies against the Axis powers. Although Japan attacked the United States first, the U.S. nonetheless pursued a "Europe first" defense policy. The United States thus left its vast Asian colony, the Philippines, isolated and fighting a losing struggle against Japanese invasion and occupation, as military resources were devoted to the European theater. During the war, the United States was referred to as one of the "Four Policemen" of Allies power who met to plan the postwar world, along with Britain, the Soviet Union and China. Although the nation lost around 400,000 military personnel, it emerged relatively undamaged from the war with even greater economic and military influence.
More InfoAmericans' eagerness to expand westward prompted a long series of American Indian Wars. The Louisiana Purchase of French-claimed territory in 1803 almost doubled the nation's area. The War of 1812, declared against Britain over various grievances and fought to a draw, strengthened U.S. nationalism. A series of military incursions into Florida led Spain to cede it and other Gulf Coast territory in 1819. The expansion was aided by steam power, when steamboats began traveling along America's large water systems, many of which were connected by new canals, such as the Erie and the I&M; then, even faster railroads began their stretch across the nation's land.
More InfoWith the 1860 election of Republican Abraham Lincoln, conventions in thirteen slave states ultimately declared secession and formed the Confederate States of America (the "South" or the "Confederacy"), while the federal government (the "Union") maintained that secession was illegal. In order to bring about this secession, military action was initiated by the secessionists, and the Union responded in kind. The ensuing war would become the deadliest military conflict in American history, resulting in the deaths of approximately 618,000 soldiers as well as many civilians. The Union initially simply fought to keep the country united. Nevertheless, as casualties mounted after 1863 and Lincoln delivered his Emancipation Proclamation, the main purpose of the war from the Union's viewpoint became the abolition of slavery. Indeed, when the Union ultimately won the war in April 1865, each of the states in the defeated South was required to ratify the Thirteenth Amendment, which prohibited slavery.
More InfoThe United States played a leading role in the Bretton Woods and Yalta conferences with the United Kingdom, the Soviet Union, and other Allies, which signed agreements on new international financial institutions and Europe's postwar reorganization. As an Allied victory was won in Europe, a 1945 international conference held in San Francisco produced the United Nations Charter, which became active after the war. The United States and Japan then fought each other in the largest naval battle in history, the Battle of Leyte Gulf. The United States worked on a secret project, known as the Manhattan Project. They eventually developed the first nuclear weapons, and tested them in the Jornada del Muerto desert about 35 miles (56 km) southeast of Socorro, New Mexico. This was known as the Trinity Test. The test was successful, which eventually led to the bombing of Japanese cities Hiroshima and Nagasaki; the Japanese surrendered on September 2, ending World War II.
More InfoFollowing the decisive Franco-American victory at Yorktown in 1781, Britain signed the peace treaty of 1783, and American sovereignty was internationally recognized and the country was granted all lands east of the Mississippi River. Nationalists led the Philadelphia Convention of 1787 in writing the United States Constitution, ratified in state conventions in 1788. The federal government was reorganized into three branches, on the principle of creating salutary checks and balances, in 1789. George Washington, who had led the Continental Army to victory, was the first president elected under the new constitution. The Bill of Rights, forbidding federal restriction of personal freedoms and guaranteeing a range of legal protections, was adopted in 1791.
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