For the better part of two centuries, the protective expanse of two oceans and fear of an America angered kept the U.S. mainland safe from foreign aggressors. What attacks did come were from within (seceding states, urban riots, the Weather Underground, Timothy McVeigh), while foreign aggressors were stopped thousands of miles off the mainland shore (Nazi Germany, Imperial Japan) or dissolved away without ever launching a strike (the Soviet Union).

That tranquil safety was broken 10 years ago this week.

The past several days have offered many retrospectives of September 11, 2001: documentaries about the attacks, histories of Osama bin Laden and al-Qaeda, interviews with political leaders, tributes to those who were killed and those who survived. To borrow from Lincoln, it is altogether fitting and proper that we should do this.

It is also fitting and proper, 10 years later, to consider the ongoing effects of 9/11 on both the attackers and the attacked.

For al-Qaeda, 9/11 was a tactical success, but it was also a spectacular strategic failure. By striking Washington and New York, bin Laden intended to cripple both the U.S. government and the economy. But government was never disrupted and the mild recession that the nation had entered in March 2001 would end just two months after the attacks.

Bin Laden also thought a 9/11-chastened United States would withdraw from involvement in the Muslim world. Instead, one month later, an angry and determined U.S. military invaded Afghanistan, driving out al-Qaeda and removing its patron, the Taliban regime, from power. Some 18 months later, America invaded Iraq. Today, the United States has heavy military presences in Afghanistan and Iraq, has conducted recent operations in Libya, Pakistan and Yemen, and intervenes throughout the region. This high level of U.S. involvement would not have happened without 9/11 as justification. One wonders if bin Laden spent his final years in Abbottabad hiding from Muslim reprisal, not American.

The ongoing effects of 9/11 on the United States are more difficult to characterize. There is one clear positive: al-Qaeda has not delivered a second attack on the U.S. mainland. Credit for this goes, in part, to the U.S. military and intelligence agencies that chased the group out of Afghanistan and around the world, killing and capturing its leaders and disrupting its finances and communications. But credit also goes to the simple recognition of terrorism’s danger and sensible responses to that danger. Following the attacks, airliner cockpit doors were hardened and are now closed during flight — a low-cost response that has made a repeat of 9/11 nearly impossible. Just as important, airline employees and the public are more vigilant — as evidenced by the foiling of shoe bomber Richard Reid.

However, increased vigilance has also contributed to a major negative for the United States.

In the months following the attacks, it was learned that government authorities had received pre-9/11 reports of Middle Eastern men in the United States acting suspiciously. From this, many people concluded that the government should have identified and prevented the strikes. But authorities receive tips every day of possible threats to national security. Almost all of them are hazy, very few have merit and even fewer clearly indicate a plot. So how to process all of those tips, and what to do when investigation results are inconclusive?

Think of national security as analogous to a burglar alarm system. Set the sensitivity too low, and you increase the risk that you will miss a break-in or fail to uncover a plot. Set the sensitivity too high and you risk lots of false alarms.

After 9/11, authorities and the public chose to set the sensitivity high and not worry about the false alarms. But false alarms can be costly. A government that will act forcefully on hazy indications of a Middle Eastern terrorist plot against the United States is also a government that will act forcefully on hazy indications that a rogue Middle Eastern government is building nuclear weapons that it could unleash on the United States. A clear connection can be drawn between the nation’s heightened alert following 9/11 and its decision to invade Iraq. The cost of that false alarm has been much American blood and treasure.

Today, 10 years removed from 9/11, America is more consumed by Middle Eastern affairs than it ever was before. We cautiously watch uprisings and revolutions, follow election results, and worry about relations between Sunni and Shia. Hopefully, in another 10 years time, September 11, 2001 will just be a day of remembrance, and the particulars of terrorism and the Middle East will be no more important to us than they were on September 10.