Defense spending

The U.S. government spends 23.6% of its budget on military spending.This is a huge amount of money. I am wondering why only 160,000 troops can be placed on the ground in Iraq while at the same time the military is said to be "stretched too thin."

Something doesn’t add up. Almost 24% of government spending! And it only gets 160,000 troops on the ground? During World War II we had milliions of men and women in uniform. And they won the war in less than 4 years. Something doesn’t add up.