The treaty that granted independence to Texas as a republic prior to its annexation by the United States was the Treaty of Guadalupe Hidalgo, signed in 1848. This treaty officially ended the Mexican-American War and recognized Texas's independence from Mexico. Following its independence, Texas functioned as an independent nation until its eventual annexation by the United States in 1845, which significantly contributed to tensions surrounding slavery and regional conflicts. The treaty had a lasting impact on U.S. territorial expansion and relations with Mexico.