Wars of liberation

The American military exists to protect American lives, not foreigners. As a rule, an American president has no moral warrant to sacrifice American troops to save the lives of foreigners.  

Although humanitarian wars are idealistic, I think they're generally unethical. The justification for having a military is national defense. And the justification of national defense is an extension of self-defense. 

I have a duty to protect my dependents. I have a duty to take a bullet for my family. I don't have a prima facie duty to take a bullet for a stranger, or even a neighbor. 

However, self-defense sometimes requires a common defense, where we pool our collective resources. An individual can't do it alone. And that's the rationale for some military alliances. Say my country and your country share a common enemy. My country can't defeat the enemy singlehandedly, and your country can't defeat the enemy singlehandedly, but if we combine forces, then our combined forces can defeat our common enemy. So we're doing each other a favor. 

The principle in that case is that I'm prepared to take a bullet for you if you're prepared to take a bullet for me. I will defend your family if you defend my family. So that's predicated on mutual risk and reciprocity. 

Humanitarian wars violate that principle. It is wrong to get our soldiers killed to prevent foreigners from getting killed. That's because there's no reciprocity. The foreigners don't return the favor. 

It's morally wrong to treat American lives as less valuable than foreign lives. It's morally wrong for a president to send an American soldier to his death, thereby depriving his own relatives, &c., to save a stranger. For his own relatives have a prior claim on his presence in their lives. 

From a surfeit of altruism, you can voluntarily risk your life to save a stranger, but that's not obligatory. And you may have prior obligations to friends and family. Social duties are concentric. 

The justification for foreign wars is to defend vital American interests. Admittedly, that justification can be easily abused by stretching what counts as a vital American interest.