We were wrong because we ignored world history. There was a reason that Afghanistan — occupied over the years by the British, then by the Soviets — was already known as “the graveyard of empires.” For cultural and geographic reasons, no would-be conqueror of the country has ever fully subdued its people. Responding to the 9/11 attack was not necessarily America’s big mistake. Staying and trying to recreate Afghanistan in something like our own image was the crucial error, both hubristic and well-intentioned — we thought we could be the conquerors who left the country better than we found it. We are not.

We were wrong, too, because we ignored our own history. By the time 2001 arrived, the memories of America’s misadventures in Vietnam had mostly faded, pushed down the memory hole by the end of the Cold War and U.S. battle victories over a series of weaker foes, including Iraq during the first Gulf War in 1991. The military establishment turned its attention in the late 1970s and 1980s to the task of confronting the Soviet Union, forgetting whatever it had learned about counterinsurgency wars. America’s leaders were prepared for tank battles and seizing capitals — and were less ready to deal with guerilla warfare. The tactical lessons of Vietnam might have helped had they been implemented earlier, but Americans also ignored the bigger strategic lesson: that it doesn’t ultimately serve U.S. interests to get bogged down, thousands of miles from home, fighting rebel guerillas on their own land. We’re bad at it.

We were wrong, finally, because the real enemy — the stateless terrorists of Al Qaeda — were not the opponents we wanted or were prepared to fight.