We can’t win a fight when they aren’t fighting us

I may not know much about policy and war and such but it does seem to me that it’s hard to win a war when the enemy is not fighting us but each other. If the Iraqis had gotten involved in our civil war, they couldn’t win because we weren’t fighting them. And we sure in hell weren’t going to listen to anyone who tried to negotiate a peace. North and South each wanted victory to support their world view and would take nothing less. That’s why we ended up in the war in the first place.  So why do we think we can have victory in Iraq when the people there are fighting each other and our soldiers are just bodies getting in the way of their killing each other?