The historic event marked by the annexation of Texas by the United States in 1845 was a key turning point in American history. Texas, having gained independence from Mexico in 1836, sought to join the Union, which was controversial due to the implications for slavery and relations with Mexico. The annexation contributed to tensions that eventually led to the Mexican-American War (1846-1848). It represented a significant expansion of U.S. territory and fueled the ongoing debate over slavery in new states, shaping the nation’s political landscape in the decades that followed.