Afghanistan is the latest is a string of American military failures since World War II: Korea, Vietnam, Lebanon, Iraq I (Saddam could have been removed but wasn’t), Somalia, 9/11 (a failure in itself), Iraq II, and Afghanistan. (Have I missed any?)
Why the failures? A combination of impetuousness and lack of resolve. Both go with the U.S. system of governance, which (except for World War II) results in frequent shifts of direction and is unduly beholden to “popular” (i.e., media-driven) opinion.
This will not change. It will only get worse. Unless there arises an immediate, existential threat (as in 1941). It must be a threat that is clearly dangerous enough to stiffen the resolve of U.S. (and Western) leaders and to overcome the anti-war, anti-defense bias of the media. But, even then, a sudden burst of resolve by U.S. (and Western) leaders may not be enough. Given technological advances since 1941, an enemy could probably cripple the West (e.g., see EMP) before U.S. and NATO forces and countermeasures can be mobilized.
In sum, monolithic regimes (e.g., China) can play the long game. The West cannot because of its “democratic” politics. Even a Churchill, if one were to arise, probably couldn’t salvage “democracy”.
But by the time that China (or an alliance of convenience led by China) is ready to bring the West to its knees, an outright attack of some kind won’t be necessary. The cultural and political rot will have burrowed so deeply into the the West’s psyche that World War III will be a walkover. A sniveling, hand-wringing affair presaged by Biden’s performance in withdrawing from Afghanistan and blaming others for his own failure.
And it won’t be a walkover for the West.