Oklahoma, with a name derived from the Choctaw Indian words okla, meaning "people," and humma, meaning "red," has a history of human occupation dating back 15,000 years. The first Europeans to visit the region were Spanish explorers in the 16th century, and in the 18th century the Spanish and French struggled for control of the territory. The United States acquired Oklahoma from France in 1803 as part of the Louisiana Purchase.
After the War of 1812, the U.S. government decided to remove Indian tribes from the settled eastern lands of the United States and move them west to the unsettled lands of Oklahoma, Kansas, and Nebraska. In 1828, Congress reserved Oklahoma for Indians and in 1834 formally ceded it to five southeastern tribes as Indian Territory. Many Cherokees refused to abandon their homes east of the Mississippi, and so the U.S. Army moved them west in a forced march known as the "Trail of Tears." The uprooted tribes joined Plains Indians that had long occupied the area, and Indian nations with fixed boundaries and separate governments were established in the region.
During the American Civil War, most tribes in Indian Territory supported the South. With the defeat of the Confederacy in 1865, the territory was placed under U.S. military rule. White cattlemen and settlers began to covet the virgin ranges of Oklahoma, and after the arrival of the railroad in the 1870s, illegal white incursion into Indian Territory flourished. Most of these "Boomers" were expelled, but pressure continued until the federal government agreed in 1889 to open two million acres in central Oklahoma for white settlement. At noon on April 22, 1889, a pistol shot signaled the opening of the new land, and tens of thousands of people rushed to stake claims. Those who had already made illegal entry to beat the starting gun were called "Sooners," hence Oklahoma's state nickname. The following year, the region was divided into Indian Territory and Oklahoma Territory.
In 1907, Congress decided to admit Indian Territory and Oklahoma Territory into the Union as a single state, with all Indians in the state becoming U.S. citizens. Representatives of the two territories drafted a constitution, and on September 17, 1907, it was approved by voters of the two territories. On November 16, Oklahoma was welcomed into the United States by President Theodore Roosevelt.
Oklahoma initially prospered as an agricultural state, but the drought years of the 1930s made the state part of the Dust Bowl. During the Depression, poor tenant farmers known as "Okies" were forced to travel west seeking better opportunities. In the 1940s, prosperity returned to Oklahoma, and oil production brought a major economic boom in the 1970s.