The region was originally under Spanish colonial rule beginning in the mid-1700s, a role that passed on to Mexico when the latter nation won its war of independence against Spain in 1821. In 1835, American settlers in Texas, discontent with Mexican rule, launched a revolution against the Mexican government, and upon their success in 1836 (following the infamous massacre at the Alamo and the decisive rout of the Mexicans at the Battle of San Jacinto) formed the independent Republic of Texas. As such, the Republic existed as an independent nation for nine years before it was annexed to the United States and admitted to the Union as the 31st state on December 29, 1845.