Manifest Destiny assumed that God had granted all land between the Atlantic and Pacific Oceans to the United States. Thousands settled in Texas in the 1840s and traveled west on the dangerous Oregon Trail. Settlers displaced Native Americans who had lived on the Great Plains for centuries. James K. Polk was elected in 1844 on a pro-expansion platform and sought to acquire California and Texas from Mexico. When Mexico refused to sell California, tensions rose and Polk provoked war by sending troops to the Rio Grande, allowing him to acquire these territories in the Treaty of Guadalupe Hidalgo in 1848.