Global evil does not seem limited to just ISIS. There are multiple examples of horrible genocide and humanitarian abuse around the world. If the issue is terrorism and the threat to the free world through terrorist attacks, I honestly don't know enough to say one way or another whether the presence of troops and their effects on containing ISIS is justified. On the other hand, I think we were totally mislead on the Iraq war that cost 5,000 American lives, not to mention the cost and the disabled wounded.