In 1845, the Republic of Texas was annexed to the United States of America, becoming the 28th U.S. state. Border disputes between the new state and Mexico, which had never recognized Texas independence and still considered the area a renegade Mexican state, led to the Mexican–American War (1846–1848). When the war concluded, Mexico relinquished its claim on Texas, as well as other regions in what is now the southwestern United States.Texas' annexation as a state that tolerated slavery had caused tension in the United States among slave states and those that did not allow slavery. The tension was partially defused with the Compromise of 1850, in which Texas ceded some of its territory to the federal government to become non-slave-owning areas but gained El Paso.