In a nutshellIn reacting to the apparent pullback in Fallujah, Glenn Reynolds, it seems to me, sums up the basic instinctual difference between right and left on foreign policy:
The besetting sin of liberalism is the refusal to learn the Machiavellian lesson that shedding some blood can, in some circumstances, reduce the total amout of blood shed. The besetting sin of conservatism is its deep belief that when brute force fails, you probably aren't using enough.