| February 19, 1846 | The Republic of Texas is officially declared at an end. |
| April 25, 1846 | A border skirmish near Brownsville marks the beginning of the U.S. war with Mexico. |
| May 08, 1846 | The Battle of Palo Alto, the first major fight of the Mexican War, results in a U.S. victory. |
| May 09, 1846 | Gen. Zachary Taylor defeats the Mexicans at Resaca de Ia Palma. |
| May 12, 1846 | Norris Cuney, one of the most prominent black men in Texas, is born a slave in Waller County. |
| September 21, 1846 | Ranger Capt. Robert Gillespie dies leading a charge on the Bishop's Palace in Monterrey during the Mexican War. |