Both sides were assholes really. Mexico originally allowed Americans to immigrate to the Texas region because Mexico Government wanted them to cull/exterminate the native American population and act as a buffer state to the US, which the American immigrants were highly effective at doing.

Then the Texans got pissed that Mexico wouldn't let them own slaves after they helped clear the lands. There were no heroes in this part of history or many other parts, a bulk of human history and modern day are just groups of people acting selfishly with disregard for other human life.