Part of the series "Ten Lessons Since the 9/11 Attacks," in which CFR fellows identify the top threats and responses going forward. Read more in the series.
An important lesson of 9/11 is the prohibitive cost of absolute security in a globalized world. To contain terrorism is one thing, but ambitions beyond containment have posed crushing burdens since. Americans will have to learn to live with a chronic threat of lower-level terrorism, or we will go bankrupt trying to recreate the immunity so many felt before 9/11.
Mass civilian deaths at the hands of foreign enemies were a new experience for most Americans in 2001. Wide oceans and friendly neighbors made war an abstraction for most, and something close to complete security from attack was widely taken for granted. When this assumption collapsed, many wanted it back. The impulse to restore the sense of security lost on 9/11 encouraged sweepingly ambitious war aims in the ensuing conflict: The Bush administration announced its intention to eliminate all terrorism of global reach and launched two wars in pursuit of this aim.
Ten years later, Osama bin Laden is dead and his organization is reeling. The prospects of mass casualty attacks on the 9/11 scale are receding as al-Qaeda central weakens, and it may be increasingly possible to contain bin Laden's successors with low-key espionage and standoff attacks by drones or commandos.
But if so, these efforts will represent containment, not eradication. Lesser terrorists will remain. Al-Qaeda's own regional affiliates in Yemen and Somalia are growing, and anti-Western militant groups in Pakistan and elsewhere threaten Americans. Ten years of warfare have suppressed the most virulent enemy in al-Qaeda central, but it has not ended terrorism per se. Certainly we can no longer afford large-scale stabilization efforts for the next places where an al-Qaeda affiliate or ally or successor may seek haven, which will leave them with an ability to kill Americans, even if they cannot manage to do so on a 9/11 scale.
The net result is a need for us to live with diminished ambitions for security. We can probably prevent another 9/11. But we cannot reasonably expect to prevent other, smaller attacks from new havens in Yemen or Somalia or elsewhere. And we will have to learn to accept the resulting degree of chronic but low-level threat in a world where absolute security is unattainable.