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.
Following 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.
More InfoFrom 1820 to 1850, Jacksonian democracy began a set of reforms which included wider white male suffrage; it led to the rise of the Second Party System of Democrats and Whigs as the dominant parties from 1828 to 1854. The Trail of Tears in the 1830s exemplified the Indian removal policy that forcibly resettled Indians into the west on Indian reservations. The U.S. annexed the Republic of Texas in 1845 during a period of expansionist Manifest destiny. The 1846 Oregon Treaty with Britain led to U.S. control of the present-day American Northwest. Victory in the Mexican–American War resulted in the 1848 Mexican Cession of California and much of the present-day American Southwest.The California Gold Rush of 1848–49 spurred migration to the Pacific coast, which led to the California Genocide and the creation of additional western states. After the Civil War, new transcontinental railways made relocation easier for settlers, expanded internal trade and increased conflicts with Native Americans. In 1869, a new Peace Policy nominally promised to protect Native Americans from abuses, avoid further war, and secure their eventual U.S. citizenship. Nonetheless, large-scale conflicts continued throughout the West into the 1900s.
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 InfoDuring the Seven Years' War (known in the United States as the French and Indian War), British forces seized Canada from the French, but the francophone population remained politically isolated from the southern colonies. Excluding the Native Americans, who were being conquered and displaced, the 13 British colonies had a population of over 2.1 million in 1770, about a third that of Britain. Despite continuing, new arrivals, the rate of natural increase was such that by the 1770s only a small minority of Americans had been born overseas. The colonies' distance from Britain had allowed the development of self-government, but their unprecedented success motivated monarchs to periodically seek to reassert royal authority.
More InfoThe United States fought Indian Wars west of the Mississippi River from 1810 to at least 1890. Most of these conflicts ended with the cession of Native American territory and their confinement to Indian reservations. This further expanded acreage under mechanical cultivation, increasing surpluses for international markets. Mainland expansion also included the purchase of Alaska from Russia in 1867. In 1893, pro-American elements in Hawaii overthrew the monarchy and formed the Republic of Hawaii, which the U.S. annexed in 1898. Puerto Rico, Guam, and the Philippines were ceded by Spain in the same year, following the Spanish–American War. American Samoa was acquired by the United States in 1900 after the end of the Second Samoan Civil War. The U.S. Virgin Islands were purchased from Denmark in 1917.
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