Obviously foreign invasions were not purely private enterprises. But American history is full of private interests pushing for war, the American Revolution itself was caused in large parts by the American private sector being much more enthusiastic to ethnically cleanse the land from natives and steal their land than the crown.
Private interests lobbying the US Government isn't really corruption, it is the way things are sadly intended to work.
My point is that the reason these atrocities are made by the government and not private companies is only that the government prevents the private sector from committing them. So giving power to the private sector instead of the government in general is not a good course of action despite these events because there is no reason to believe it is any less enthusiastic to do atrocious things.