USA is not a single entity with a single voice.

Historically, generals of strong empires tend to go fight rebellions or weaker enemy states for prolonged time even if they could destroy them quickly. They do that to maintain power, or the empire will have no more enemies and the military's influence drops.

I'm not saying that's what happened in this case, but that is one of many reasons American entities (military, politicians, whatever) act against some other Americans' interests.