Furthermore the doctrine of mutually assured destruction requires that you be able clearly to identify the source of a strategic first strike. This was easy when we and the Soviets were the only one's on the planet with that capability. Proxy wars popped up all over the place, police actions, low intensity conflicts, and the occasional outright invasion in places where both sides could fight it out without risk of triggering a strategic response.
The confluence of proliferation and terrorism threw that equation totally out of balance. Everyone seemed to understand that "the world changed on 9/11" but now they don't seem to grasp what exactly it is that changed.
The bad guys are doing everything in their power to develop stealth first strike capability. A strike with no clear origin but with a devastating impact. This is the published strategy of the Jihadi's. As much as people like to beat their chests and say 'we will nuke Mecca' or 'we will turn Iran to glass', the Jihadi's know that it's just not that simple. Even under the gravest of circumstances it is unlikely that we or our allies will indiscriminately murder millions of people. It wouldn't stop the terrorists even if we did.
The world did, indeed, change on 9/11 but we have gone back to sleep. The rules we lived by in the past, such as not attacking unless there was an imminent threat, or placing the civil rights of non-citizens ahead of national security (not profiling people), have now become suicidal. They just won't work any longer.
There were two things that kept the Soviets from coming after us directly. There would be no way to hide the origin of the attack and their communist system lacked the economic power to win the global resources race and thereby starve away our ability to respond. (Note that Ronnie Reagan finally pushed them over the edge by out spending them and not by nuking their cities) The Jihadi's have adopted a strategy that bypasses both of those problems but ONLY if we sit back and wait for them to come to us. We have no choice but to go after them aggressively both at home and abroad.
Another rant. Sometimes I just can't stop myself.
The Islamofascists are completely different, they place absolutely no value whatsoever on human life, not even their own. A suicidal madman is something that was never even a consideration a few decades ago.