The rules of warfare:
1. Never humanize your enemy.
2. Kill your enemy until he stops killing you.
3. There are no rules in war.
You are right. The problem with modern western warfare is that we never completely wipe out the enemy,and they continue to rise up again and again.The end result is more war instead of just finishing the battle once and for all.
Sadly the US is constrained by a bunch of liberal lawyers in the JAG core.