1. Never humanize your enemy.
2. Kill your enemy until he stops killing you.
3. There are no rules in war.
Rule #2 needs a minor revision. Sapping your enemy's will to fight can be done in many more ways than simply killing. (Heck, look at the incredibly good job the MSM does at sapping our will to fight, particularly by violating Rule #1.) Sun Tzu, and anyone who has actually fought in a battle, will tell you that it is FAR better to win without firing a shot.
(However, if clever diplomacy, sneaky tricks, ruthless espionage, and overt threats don't work, few methods are more reliable than quickly and efficiently taking out far more of them than they take from us.)