There are already more than 100,000 international troops in Afghanistan working with 200,000 Afghan security forces and police. It adds up to a 12-1 numerical advantage over Taliban rebels, but it hasn't led to anything close to victory.

Now, the top U.S. and NATO commander in Afghanistan is asking for tens of thousands more troops to stem the escalating insurgency, raising the question of how many more troops it would take to succeed.

"The U.S. and its allies already have ample numbers and firepower to annihilate the Taliban, if only the Taliban would cooperate by standing still and allowing us to bomb them to smithereens," said Andrew Bacevich, a professor of international relations and history at Boston University, and one-time platoon leader in Vietnam.