On this 9/11 anniversary, I sense a dangerous complacency creeping into public discourse. Because we have not been hit again on the home front since 2001, many now assume that the danger is exaggerated or even nonexistent. The war in Afghanistan, launched in direct response to the 9/11 attacks, is now turning increasingly unpopular.

For those who want a wake-up call to the dangers that still exist, I recommend picking up Andrew Krepinevich’s book 7 Deadly Scenarios. A retired army colonel, Andy is head of the Center for Strategic and Budgetary Assessments and a longtime Pentagon consultant who has worked closely over the years with strategy guru Andy Marshall (who first called our attention to the “revolution in military affairs” brought about by information technology). He is, in short, a well-respected analyst and hardly an alarmist, but anyone who reads his book will have trouble sleeping at night.

Andy isn’t in the prediction business, per se. What he does is offer scenarios that are quite plausible and then asks us to think about a response. Scenarios such as the collapse of Pakistan, with the attendant possibility that some of its nuclear weapons fall into jihadist hands. Or—the truly nightmarish scenario—”War Comes to America”: terrorists get their hands on Russian nuclear weapons and start detonating them in major American cities. Those are only two of the seven deadly scenarios he sketches. What they all have in common is the targeting of American vulnerabilities in ways extremely difficult and costly for us to address.

If you want to know why we need to have a “forward” posture in the war on terrorism—why we need to fight as much as possible in Afghanistan and Iraq, not in the streets of America; why we can’t leave the task of defending us to law-enforcement agencies, which use traditional legal mechanisms—read Krepinevich’s book.