In 1776, in Philadelphia, the Second Continental Congress declared the independence of the colonies as the "United States". Led by General George Washington, it won the Revolutionary War. The peace treaty of 1783 established the borders of the new sovereign state. The Articles of Confederation established a central government, but it was ineffectual at providing stability as it could not collect taxes and had no executive officer. A convention wrote a new Constitution that was adopted in 1789 and a Bill of Rights was added in 1791 to guarantee inalienable rights. With Washington as the first president and Alexander Hamilton his chief adviser, a strong central government was created. Purchase of the Louisiana Territory from France in 1803 doubled the size of the United States.
Encouraged by the notion of manifest destiny, the United States expanded to the Pacific Coast. While the nation was large in terms of area, its population in 1790 was only four million. Westward expansion was driven by a quest for inexpensive land for yeoman farmers and slave owners. The expansion of slavery was increasingly controversial and fueled political and constitutional battles, which were resolved by compromises. Slavery was abolished in all states north of the Mason–Dixon line by 1804, but states in the south continued the institution, to support the kinds of large scale agriculture that dominated the southern economy. Precipitated by the election of Abraham Lincoln as president in 1860, the Civil War began as the southern states seceded from the Union to form their own pro-slavery country, the Confederate States of America. The defeat of the Confederates in 1865 led to the abolition of slavery. In the Reconstruction era following the war, legal and voting rights were extended to freed male slaves. The national government emerged much stronger, and gained explicit duty to protect individual rights. However, when white southern Democrats regained their political power in the South in 1877, often by paramilitary suppression of voting, they passed Jim Crow laws to maintain white supremacy, as well as new state constitutions that legalized discrimination based on race and prevented most African Americans from participating in public life.
The United States became the world's leading industrial power at the turn of the 20th century, due to an outburst of entrepreneurship and industrialization and the arrival of millions of immigrant workers and farmers. A national railroad network was completed and large-scale mines and factories were established. Mass dissatisfaction with corruption, inefficiency, and traditional politics stimulated the Progressive movement, from the 1890s to the 1920s, leading to reforms, including the federal income tax, direct election of Senators, granting of citizenship to many indigenous people, alcohol prohibition, and women's suffrage. Initially neutral during World War I, the United States declared war on Germany in 1917 and funded the Allied victory the following year. After the prosperous Roaring Twenties, the Wall Street Crash of 1929 marked the onset of the decade-long worldwide Great Depression. President Franklin D. Roosevelt implemented his New Deal programs, including relief for the unemployed, support for farmers, social security, and a minimum wage. The New Deal defined modern American liberalism. Following the Japanese attack on Pearl Harbor, the United States entered World War II and financed the Allied war effort, and helped defeat Nazi Germany and Fascist Italy in the European theater. Its involvement culminated in using newly American invented nuclear weapons on Hiroshima and Nagasaki to defeat Imperial Japan in the Pacific War.
The United States and the Soviet Union emerged as rival superpowers in the aftermath of World War II. During the Cold War, the two countries confronted each other indirectly in the arms race, the Space Race, propaganda campaigns, and proxy wars. In the 1960s, in large part due to the strength of the civil rights movement, another wave of social reforms was enacted which enforced the constitutional rights of voting and freedom of movement to African Americans. The Cold War ended when the Soviet Union was officially dissolved, leaving the United States as the world's sole superpower. Foreign policy after the Cold War has often focused on conflicts in the Middle East, especially after the September 11 attacks. Early in the 21st century, the United States experienced the Great Recession and the COVID-19 pandemic, which had a negative effect on the local economy.
Main articles: Prehistory of the United States, History of Native Americans in the United States, and Pre-Columbian era
See also: Native Americans in the United States
Approximate location of the ice-free corridor and specific Paleoindian sites (Clovis theory)
It is not definitively known how or when Native Americans first settled the Americas and the present-day United States. The prevailing theory proposes that people from Eurasia followed game across Beringia, a land bridge that connected Siberia to present-day Alaska during the Ice Age, and then spread southward throughout the Americas. This migration may have begun as early as 30,000 years ago and continued through to about 10,000 years ago, when the land bridge became submerged by the rising sea level caused by the melting glaciers. These early inhabitants, called Paleo-Indians, soon diversified into hundreds of culturally distinct nations and tribes.
This pre-Columbian era incorporates all periods in the history of the Americas before the appearance of European influences on the American continents, spanning from the original settlement in the Upper Paleolithic period to European colonization during the early modern period. While the term technically refers to the era before Christopher Columbus' voyage in 1492, in practice the term usually includes the history of American indigenous cultures until they were conquered or significantly influenced by Europeans, even if this happened decades or centuries after Columbus's initial landing.[4