As a result of the U. S. Mexican War, the southern boundary of Texas was-

The war officially ended with the February 2, 1848, signing in Mexico of the Treaty of Guadalupe Hidalgo. Mexico gave up all claims to Texas and recognized the Rio Grande as America's southern boundary.

Explanation: Hope this helped!! :D

one of the main reasons was definitely slavery. back in 1861, republican abraham lincoln was elected and ended up being a major influence in the slavery business. slavery greatly affected the texas economy because back in 1845 during the annexation of texas, slaves became a big part of the texas population. many texans that were in favor of the secession influenced groups through party ties.

other sources of text

explanation:

this can be magazines, news reports, scholarly articles, textbooks, research papers etc.