The following is gleaned from my studies of "Sun Tzu's The Art of War."
Know yourself and know your enemy. The general who knows himself and his enemy need not fear the outcome of 100 battles. The General who is unsure about either will not emerge victorious. Even if the war is won the occupation will be lost.
Do not give into to irrational feelings. The general that does can be manipulated.
Do not fight a war unless the survival of the nation is at stake.
Thou shall not fight wars on credit. If a war is to be fought, generate the revenue required in a single levy, a protracted war can exhaust a nations treasury.
Do not base a war on false data, or what God seems to say, only one thing matters in a war hard intelligence. Sun Tzu devoted an entire chapter in his treatise on the value of spies.
Treat the defeated enemy as you would want to be treated yourself. A captured enemy can become an ally if treated with kindness.
I could go on and on but everything in Sun Tzu's treatise comes back to this point. Not only is Sun Tzu's treatise an excellent guide for war, it can be lived as a guide to life.
I am not surprised that Iraq is still a quagmire even after the U.S. pulled out. it was fought on faulty data.