America, in the large sense, was once populated by Amerindian peoples. In the United States those that remain are known as Native Americans, or American Indians. With populations once in the tens of millions, most led tribal, hunter-gatherer lifestyles. Later some settlements and political enclaves based on agriculture, such as the Five Nations of the Northeast and the Pueblo peoples of the Southwest, developed. European settlement of the area began in the 16th century with the establishment of St. Augustine in Florida by missionaries from Spain. The Spanish also established colonies in much of the Southwest, California, Texas and Louisiana as extensions of their North American stronghold in Mexico. Meanwhile, French missionaries and settlers from Canada made inroads into the Great Lakes region of the Midwest and down the Ohio and Mississippi river systems. The colony of Louisiana, centered around New Orleans, subsequently became a French stronghold in the Gulf of Mexico. Smaller colonies were established by the Netherlands in present-day New York, by Sweden on the Atlantic Coast, and by Russia in Alaska and the Pacific Northwest.

The founding of British colonies in Virginia and Massachusetts in the early 17th century marks the beginning of what we now know as the United States of America. By the early 18th century, 13 colonies ranged along the Atlantic coast from Georgia to present-day Maine. It also marked the beginning of the displacement of the Native American population westward and the extinction of many others, as well as the end of the embryonic Dutch and Swedish footholds. There were distinct differences between the British settlers of the north and south: the southern areas, because of a longer growing season, had richer agricultural prospects, especially for cotton and tobacco. Large plantations developed with most of the labor being provided by African slaves, as was typical of most of Central and South America, and for the same reasons. The Northern colonies on the other hand developed as mercantile societies modeled after the "home" country, Britain. This dichotomy would later lead to a civil war.

By the late 18th century, the colonials were divided between loyalists and those who wished to separate from Britain. The revolutionaries carried the day and declared independence on July 4, 1776. This precipitated a Revolutionary War against the British, and this date has become a national holiday commemorating the establishment of the country. The American Constitution was inspired by Enlightenment-era ideas about government and human rights and remains a model that is considered by newly forming democracies around the world. The late 18th and early 19th century were characterized by the stabilization of the Federal government and the first steps of Western expansion. Many Americans felt a Manifest Destiny to expand all the way to the Pacific ocean. Territories in the Midwest were added as new states, and the Louisiana Purchase of 1803 gave the United States nominal control of former French territory along the Mississippi River, and stretching out to the Pacific Ocean. Much of this area was however contested by Britain, especially in the northeast. Florida was purchased in 1813 from the Spanish; American settlers in Texas and California both rebelled against the Mexican government, and these areas were added to the Union. The Mexican-American War of the 1840s won the territories of Arizona and New Mexico, giving the continental US the rough outlines it has today. The marginalization of the Native Americans, and their concentration in the west by treaty, military force, and by the inadvertent spread of European diseases, continued apace.

By the mid-19th century the differences between North and South had become severe. Though slavery was not the only issue between the two, it was an important one. In particular, the question of whether the new states in the west would be "slave" or "free" became a critical issue. By the 1860s, the Southern states decided to secede from the Union and civil war broke out. It was one of the bloodiest conflicts in history, costing hundreds of thousands of lives. With the victory of the North a single country was maintained. While slavery was abolished, the former slaves by and large remained an economic and social underclass in the South. The late 19th century saw the USA cementing its power on the continent and making tentative expansions abroad. Alaska was purchased from the Russians in the 1870s, and Hawaii was annexed in the 1890s. The Spanish-American War gained the first "colonial" territories: the Philippines and Cuba (both later granted independence) and Puerto Rico (which remains by choice a US territory). In the Eastern cities of the United States, an immigration boom had begun. Southern and Eastern Europeans, especially Italians, and Slavs, including many Jews fleeing Russian pogroms, joined Irish refugees to become a cheap labor force for the country's growing industrialization. Many Southern African-Americans fled rural poverty for the relative security of industrial jobs in the North. Other immigrants, including many Scandinavians and Germans, moved to the now-opened territories in the West and Midwest, where land was available for free to anyone who would develop it. A network of railroads, most notably the transcontinental railroad which runs from the Atlantic to the Pacific, crisscrossed the country, allowing faster movement of people and materials, and thus accelerating development. The Chinese Exclusion Act of 1882 prevented Chinese and other Asian groups from immigrating in large numbers in the late 1800's and early to mid 1900's.

With its entrance into World War I near the end of the conflict, the United States truly established itself as a world power. The creation of real wealth grew rapidly in this period, yet in the Roaring 20s stock speculation created an immense "bubble" which, when it burst in October of 1929, created economic havoc, known as the Great Depression, across the country and around the world. This crisis exacerbated the disaffection among the working classes in the United States and around the world and led to a rise in socialist thinking that was to have a large effect on the rest of the century. In late 1941 the United States entered World War II, which had begun in Europe in 1939. In Alliance with the United Kingdom and the Soviet Union, the USA helped defeat the fascist regimes in Italy, Germany, and Japan. At the end of this war of unprecedented scale, the United States, because of its relative isolation and power, became the dominant economic power in the world, producing nearly half of the world's production. The Soviet Union, a former ally, though now devastated from the war was still a powerful military power, and became a rival of the United States and the other "western" countries, giving rise to what is now known as the Cold War. Also at the end of the war, African Americans, who had long suffered de facto disenfranchisement, demanded equal rights, with widespread demonstrations. This, and the status of women and other "overdue" societal changes that had been contained by the effort of the war, flowered into a virtual revolution. The unpopular war in Vietnam, a by-product of the Cold War, added to the social strife. Taken together these changes led to significant change in the country: the economic and political conditions for African Americans substantially improved; a majority of women entered the workplace, and this had a powerful effect on home life, the workplace and the economy.