President John Tyler, had tried from 1844 to 1845 to have the Republic of Texas annexed to the United States. However, the proposal did not get sufficient votes in the U.S. senate due to concerns of the annexation potentially starting a war with Mexico.
When President James Knox Polk became president he supported the annexation of Texas and the proposal to purchase land from Mexico so that the United States could be expanded to the Pacific Ocean. On December 29, 1845, Texas was admitted as a state.