Texas

 
Historical Timeline
 1844 Congress narrowly approves the annexation of Texas. 
 1845 Slaveholding Texas is annexed to the United States and admitted as a slave state, thus sparking the Mexican War.
 1848 Mexico cedes more than half of its territory to the U.S., including New Mexico and California in addition to Texas.

Slave Populations:

 

bullet1830: 58,161
bullet1860: 182,566