The history of the United States began with the arrival of the first people in the Americas around 15,000 BC. European colonization started in the late 15th century, and most colonies in what would become the United States were settled after 1600. The thirteen British colonies grew in population and were established along the Atlantic Coast. The Southern Colonies relied on slave labor for agriculture. Conflict with Britain over taxes led to armed resistance and eventually the declaration of independence in 1776. The United States won the Revolutionary War and established a new government with the Constitution in 1789. The country expanded westward, doubling its size with the Louisiana Purchase in 1803.