On October 13, 1845, the electorate of the Republic of Texas voted overwhelmingly to ratify annexation to the United States and approve a newly drafted state constitution. Motivated by severe public debt, persistent border tensions with Mexico, and alignment with American expansionism, Texas voters took the final popular step in transforming the sovereign frontier republic into an American state.
After the referendum, Congress approved and President James K. Polk signed the Joint Resolution for the Admission of the State of Texas into the Union on December 29, 1845, making Texas the nation’s 28th state. The annexation redrew the geopolitical map of North America and deepened a diplomatic crisis with Mexico, which had never recognized Texas independence and continued to regard it as a rebellious province.
The unresolved dispute over whether Texas’s southern boundary lay at the Nueces River, as Mexico claimed, or the Rio Grande, as the United States and Texas claimed, helped precipitate the Mexican-American War in 1846. The conflict ultimately confirmed the Rio Grande boundary and carried the United States’ expansion to the Pacific coast.
