What happened in 1846?

Answer 1

The Mexican-American War was a conflict between the United States and Mexico, fought from April 1846 to February 1848. ... It stemmed from the annexation of the Republic of Texas by the U.S. in 1845 and from a dispute over whether Texas ended at the Nueces River (the Mexican claim) or the Rio Grande (the U.S. claim).

Answer 2

As related to the American Civil War, 1846 was the start of the Mexican War. This war opened up more land that could become new States, which raised the debate over Slave State versus Free State in the next Presidential election. The Mexican War(1846-1848) was also important as a training ground for many of the officers who would lead both Union and Confederate armies in the Civil War.