On this day in 1846, Congress granted the request of then-President James K. Polk to declare war on Mexico. The conflict centered on territorial claims to Texas, which had been an independent republic since it left Mexico in 1836.
Mexico had threatened war if the U.S. made any move to annex Texas. But the warnings were ignored when the U.S. and the new Republic agreed to a treaty of annexation, which Congress passed in March 1845.
In July 1845, Polk sent troops into disputed territory between the Nueces River in Texas and the Rio Grande. Later, the army advanced to the mouth of the Rio Grande, its future Southern border. Mexico saw that as a violation of their sovereignty and sent their own troops to the northern side of the Rio Grande. Polk made his request to Congress, and hostilities commenced. The war would go on for two years before a settlement was reached in the Treaty of Guadalupe Hidalgo in 1848.
The victorious U.S. ended up getting much more than Texas. The Rio Grande was made the permanent boundary between the two countries, and California and New Mexico became part of the U.S. in exchange for $15 million dollars and the settlement of all legal claims against Mexico by U.S. citizens.
You can learn more about the Mexican-American war at History.com.
