Ivo Daalder: Remembering Sept. 12, 2001

Ivo Daalder is U.S. ambassador to the North Atlantic Treaty Organization.

The shock and horror of 9/11 is burned into all our memories. I was on an aircraft over the Atlantic that day, flying back to Washington from Brussels, when the pilot gave us the awful news and turned the plane back.

I well remember the terrible feeling I had, as many people around the world did at that moment — that I could have been on one of those planes, or that I could have been in one of those buildings. None of us was safe anymore.

On Sunday, we all remembered that day 10 years ago, when terrorists turned airplanes into weapons of mass destruction.

But we should also remember what happened the following day.

Sept. 12, 2001, the North Atlantic Council, NATO’s governing body, met in special session.

For the first time since NATO’s founding in 1949, the council decided unanimously to invoke Article 5 of the North Atlantic Treaty, saying the attack on 9/11 was not just an attack on the United States, but an attack on all the members of NATO...