Well, after 9/11, when the war on terror officially began, it was obvious that first step would be Afghanistan.
After bin Laden escaped to Pakistan, the question became who was next? Iraq or Iran?
Saddam Hussein became the next choice. Unfortunately, right after the fall of Saddam's regime, we made spectacular blunders that we are still paying for. Iraq's problems have slowed us down severely thusfar.
If we had made better strategic decisions immediately post-Saddam, Iraq would have gone much smoother, and Iran may have already been taken care of by now.
Mistakes are unavoidable. The fact that we were (and still are) sabatoged by the Left has slowed us down more than any mistakes that we've made.