That's what you call a "false equivalency." The Mexicans were actually the good guys during that conflict: The US wanted their territory to expand slavery westward. The Mexicans defended their territory to keep their black citizens free. You see, Moe, it is not opposing the interests of the US that make an adversary evil. Instead an adversary is good or evil or somewhere in between based on its values. The Confederacy valued slavery. Mexico valued a degree of freedom.