Following the passage of the Lee Resolution, on July 2, 1776, which was the actual vote for independence, the Second Continental Congress adopted the Declaration of Independence, on July 4, which proclaimed, in a long preamble, that humanity is created equal in their unalienable rights and that those rights were not being protected by Great Britain, and finally declared, in the words of the resolution, that the Thirteen Colonies were independent states and had no allegiance to the British crown in the United States. The fourth day of July is celebrated annually as Independence Day. In 1777, the Articles of Confederation established a weak government that operated until 1789.
Britain recognized the independence of the United States following their defeat at Yorktown. In the peace treaty of 1783, American sovereignty was recognized from the Atlantic coast west to 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 revolutionary 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.
Although the federal government criminalized the international slave trade in 1808, after 1820 cultivation of the highly profitable cotton crop exploded in the Deep South, and along with it the slave population. The Second Great Awakening, beginning about 1800, converted millions to evangelical Protestantism. In the North it energized multiple social reform movements, including abolitionism; in the South, Methodists and Baptists proselytized among slave populations.
Americans' 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 size. The War of 1812, declared against Britain over various grievances and fought to a draw, strengthened U.S. nationalism. A series of U.S. military incursions into Florida led Spain to cede it and other Gulf Coast territory in 1819. Expansion was aided by steam power, when steamboats began traveling along America's large water systems, 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.
From 1820 to 1850, Jacksonian democracy began a set of reforms which included wider 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 moved Indians into the west to their own 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 western migration and the creation of additional western states. After the American Civil War, new transcontinental railways made relocation easier for settlers, expanded internal trade and increased conflicts with Native Americans. Over a half-century, the loss of the American bison (sometimes called "buffalo") was an existential blow to many Plains Indians cultures. In 1869, a new Peace Policy sought to protect Native-Americans from abuses, avoid further war, and secure their eventual U.S. citizenship, although conflicts, including several of the largest Indian Wars, continued throughout the West into the 1900s.
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