https://www.slowboring.com/p/afghan-war
Since the Taliban was never the internationally recognized government of Afghanistan, one totally plausible approach to 9/11 would have been a fast military action aimed at killing top al-Qaeda and Taliban leaders, putting the Afghan opposition coalition back in charge of Kabul, and then basically leaving them to figure things out.
Another approach would have been to try to really commit wholeheartedly to the U.S.-led reconstruction of Afghanistan — to go all-in on what was called at the time “nation-building.”
The Bush administration didn’t want to take what was behind door number two for basically two reasons. One was that they were skeptical of the odds of success in a massive rebuilding effort. But the second and more important reason is that they wanted to invade Iraq. When 9/11 happened, American military preparedness was based around the 1-4-2-1 doctrine. The first 1 was the defense of the homeland. The 4 is to deter enemies in four key regional theaters. Then the 2-1 meant, to quote Fred Kaplan, that “the U.S. armed forces must have the strength to win swiftly in two near-simultaneous conflicts in those regions. The final 1 means that we must win one of those conflicts ‘decisively,’ toppling the enemy’s regime.”
So basically do a regime change operation in Iraq while also helping South Korea win a war against North Korea.
In other words, Bush had to choose. Either Iraq or Afghanistan could be War Number One, but they couldn’t both be. He chose Iraq. That should have implied taking the quick-and-dirty approach to the war in Afghanistan. But Osama bin Laden got away at Tora Bora, so the quick-and-dirty war lacked an emotionally and politically satisfying endpoint.
Given that context, he made a very fateful choice that has haunted us ever since. He adopted the expansive nation-building goal but deliberately turned the war into an economy of resources effort in order to devote maximum resources to War Number One against Saddam Hussein. But then of course he didn’t level with the public that this is what he was doing. And even though the war was sidelined in terms of American resources, it nevertheless was shot-through with maximalist goals.