The political entity now called the United States emerged from thirteen British colonies that declared independence on July 4, 1776. The Declaration of Independence, drafted primarily by Thomas Jefferson, asserted sovereignty over territory stretching from the Atlantic coast to the Appalachian Mountains. The American Revolutionary War began in 1775 and ended with the Treaty of Paris in 1783, which recognized independence and extended territorial claims west to the Mississippi River. The war itself involved conventional battles, guerrilla tactics, and foreign alliances—France entered the conflict in 1778, providing naval support and military advisors. George Washington commanded the Continental Army throughout the conflict, presiding over a force that fluctuated between poorly supplied militia units and increasingly professional regiments.
The Articles of Confederation governed the new nation from 1781 until 1789, establishing a weak central government unable to collect taxes or regulate interstate commerce. The Constitutional Convention convened in Philadelphia in 1787, producing a federal system that balanced state and national authority. The Constitution took effect in 1789 after ratification by nine states. James Madison's notes from the convention documented debates over representation, slavery, and executive power—compromises that embedded contradictions the nation would address through amendments, judicial interpretation, and civil war. Benjamin Franklin attended the convention at age 81, serving as a mediating voice among delegates. Alexander Hamilton, as the first Secretary of the Treasury, established the national bank and federal assumption of state debts, creating institutional architecture for a modern fiscal state.
Territorial expansion defined the early republic. The Louisiana Purchase of 1803 transferred 828,000 square miles from France to the United States for $15 million, doubling the nation's size. Thomas Jefferson commissioned the Lewis and Clark Expedition in 1804 to map the newly acquired territory and establish overland routes to the Pacific Ocean. The expedition, guided at critical junctures by Sacagawea, reached the Pacific coast in November 1805 and returned to St. Louis in September 1806 with botanical specimens, geographic data, and diplomatic contacts with indigenous nations. The War of 1812 arose from disputes over maritime rights and territorial ambitions in the Great Lakes region. British forces burned Washington, D.C. in August 1814, destroying the Capitol and the executive mansion. The Treaty of Ghent ended the war in December 1814 without addressing the stated causes, but established a boundary commission to settle territorial disputes along the Canadian border.
Indigenous removal policies accelerated during the 1830s. The Indian Removal Act of 1830 authorized forced relocation of southeastern nations to territory west of the Mississippi River. The Trail of Tears refers specifically to the Cherokee removal of 1838-1839, during which approximately 4,000 of 16,000 forcibly relocated Cherokee died from exposure, disease, and inadequate provisions. The Choctaw, Creek, Chickasaw, and Seminole nations faced similar removals under military supervision. Federal policy shifted from treaty negotiation to unilateral displacement as white settlement pressure intensified. Western expansion continued through the annexation of Texas in 1845, the Oregon Treaty with Britain in 1846 establishing the 49th parallel as the northern boundary, and the Mexican Cession of 1848 transferring California and the Southwest following military defeat of Mexico.
The California Gold Rush began in January 1848 when James Marshall discovered gold at Sutter's Mill. By 1849, approximately 90,000 migrants arrived in California seeking mineral wealth. By 1855, over 300,000 people had moved to California, transforming it from a sparsely populated territory to a state admitted to the Union in 1850. The influx created San Francisco as a major port, established hydraulic mining operations that reshaped river valleys, and displaced indigenous populations through violence and disease. Approximately $2 billion worth of gold was extracted during the first two decades of industrial mining.
Slavery expanded westward with the cotton economy, while northern states completed gradual emancipation by the 1840s. The Compromise of 1850 attempted to balance free and slave state admissions through popular sovereignty in new territories, but the Kansas-Nebraska Act of 1854 repealed earlier geographic restrictions, leading to armed conflict in Kansas. Frederick Douglass, who escaped slavery in 1838, published his autobiography in 1845 and became the most prominent abolitionist orator. Harriet Tubman escaped in 1849 and conducted approximately 13 missions into slave states, guiding approximately 70 people to freedom via networks of safe houses known as the Underground Railroad. The Dred Scott decision of 1857 ruled that enslaved people and their descendants could not be citizens and that Congress lacked authority to prohibit slavery in federal territories, intensifying sectional conflict.
Abraham Lincoln won the 1860 presidential election without appearing on the ballot in most southern states. South Carolina seceded in December 1860, followed by ten other states that formed the Confederate States of America. Confederate forces fired on Fort Sumter in Charleston Harbor on April 12, 1861, beginning a civil war that lasted until April 1865. The conflict mobilized over 2 million Union soldiers and approximately 750,000 Confederate soldiers. Approximately 620,000 soldiers died from combat and disease—roughly 2% of the national population. The Emancipation Proclamation took effect January 1, 1863, declaring freedom for enslaved people in rebel-held territory, transforming the war into an explicit contest over slavery. The Thirteenth Amendment, ratified in December 1865, abolished slavery throughout the territory. The Fourteenth Amendment of 1868 granted citizenship to all persons born or naturalized in the country, and the Fifteenth Amendment of 1870 prohibited racial restrictions on voting.
Reconstruction governments in southern states established public school systems, revised property laws, and elected Black representatives to state legislatures and Congress. The Compromise of 1877 withdrew federal troops from the South in exchange for Republican retention of the presidency after the disputed 1876 election. Southern states subsequently enacted laws mandating racial segregation in public facilities, transportation, and schools. The Supreme Court's Plessy v. Ferguson decision of 1896 upheld segregation under the doctrine of "separate but equal," establishing legal precedent that persisted until 1954.
Industrial expansion accelerated after the Civil War. Transcontinental railroad completion in 1869 connected Omaha to Sacramento, reducing cross-country travel from months to days. Steel production increased from 77,000 tons in 1870 to 11.2 million tons in 1900. Thomas Edison established the first electric power station in New York City in 1882, initiating urban electrification. Henry Ford introduced the moving assembly line at his Highland Park plant in 1913, reducing Model T chassis assembly time from 12 hours to 93 minutes. Annual automobile production increased from 4,100 in 1900 to 1.9 million in 1920. The Wright Brothers achieved sustained powered flight at Kitty Hawk on December 17, 1903, with a flight lasting 12 seconds and covering 120 feet.
Immigration reshaped urban demographics. Between 1880 and 1920, over 20 million immigrants entered the country, predominantly from southern and eastern Europe. Ellis Island processed approximately 12 million immigrants between its opening in 1892 and closure in 1954. The Immigration Act of 1924 established national origin quotas that restricted immigration from outside northwestern Europe. Japanese immigration to the West Coast, which peaked at 130,000 arrivals between 1901 and 1908, was restricted through the Gentlemen's Agreement of 1907 and prohibited entirely by the 1924 act.
The Great Depression began with the stock market crash of October 1929. Unemployment reached 25% in 1933. Approximately 7,000 banks failed between 1930 and 1933. Franklin D. Roosevelt assumed the presidency in March 1933, initiating programs collectively termed the New Deal. The Civilian Conservation Corps employed 3 million young men in land development projects between 1933 and 1942. The Social Security Act of 1935 established old-age pensions and unemployment insurance. The Tennessee Valley Authority constructed 16 dams between 1933 and 1944, providing electricity to rural areas previously without power. The Works Progress Administration employed 8.5 million people between 1935 and 1943 in infrastructure construction.