Correct answer choice is :
A) It became a source of conflict once Texas became a part of the United States.
Step-by-step explanation:
Dispute with Mexico started when the United States joined Texas as a state in 1845. Mexico declared that the new border between Texas and Mexico was the Nueces River, while the United States fought the border was the Rio Grande. Combat started when a patrol of U.S. troops was attacked near the Rio Grande. The 1848 Treaty of Guadalupe Hidalgo, pushed onto the remnant Mexican government, stopped the war and drove the Mexican Cession of the northern provinces of Alta California and Santa Fe de Nuevo México to the United States.