Pioneer settlers were sometimes pulled west because they wanted to make a better living. Others received letters from friends or family members who had moved west. These letters often told about a good life on the frontier. The biggest factor that pulled pioneers west was the opportunity to buy land.
Originally Spain, Great Britain, Russia, and the United States claimed the territory. In 1819, under terms of the Transcontinental Treaty, Spain ceded its claims to the territory to the United States.
