As a kid growing up in the shadow of the Vietnam War, I remember reading bumper stickers that did not just promote peace, but also indicted those who fought.  I can understand this because as Americans, our involvement in any war has always been voluntary.  We look at war as something that we can just choose to avoid.

We have never wondered if our elderly parents or grandparents were buried alive in burning rubble.
We have never stood in the window helpless, listing to our sisters' scream as a sniper's bullet ripped through her chest.
We have never cowered in the basement clutching our children to our chests while enemy shells blew apart our small home and meager belongings.

Most Americans only know of war; we don't know war.  We have the mistaken belief that we will always get to call the plays on the field.  That we can always hold war at arms length.  We cannot picture, I cannot picture, the United States under attack by invading forces.  Because of this, so many people have taken the next step of believing not only that we could manage to never engage the U.S. military in a war, but further, we could also mostly dismantle our military because we do not have a realistic need to defend ourselves from any threats.  It explains why the American psyche has been steeled against the idea of a large standing Army throughout our history.

September 11, 2001 was a wake-up call (as was December 7, 1941).  The phone rang and the caller said, "Hello, this is the outside world".  We had remained silent in the face of suffering because we could, because our fortunate geography gave us that option.  It is horrible that it took a great tragedy for us to decide to attempt to right a wrong.

This is not about the idea that we need to insert ourselves into more world conflicts.  It's to say that we should not wait until the crisis is at our doorstep.  Yes, we were late in Bosnia, but our constant involvement in the region since has prevented many minor threats from growing.  Sending aid organizations to give money to corupt governments will not prevent war.  Sending Peace Keepers into armed conflicts has repeatedly failed and lead to additional loss of life.  Who does it make sense to send, then?

WWI
WWII
Korea
Rwanda
Bosnia

What if they threw a war and the United States didn't come?  I think the answer is obvious.  "Let them eat cake", is not good foreign policy.