Why Americans lose wars There are a few things that ought to be mentioned here:
1. Waging war is a matter of costs and benefits.
2. In order to gauge whether a war is lost or won, the conditions for victory must be established.
3. Countries may lie to foreign and domestic audiences about their reasons for going to war, and their victory conditions for reasons that should be obvious.
If we look at Afghanistan with that in mind, what were the real reasons for US involvement there? What did the US expect to gain, and at what cost?
It probably comes to no surprise to you that I am deeply skeptical about the US' stated reasons for going to war: 'the war on terror' and 'spreading democracy'. I think these are both completely unbelievable and clearly fabricated for PR purposes, quite similar to how the US did not invade Iraq over suspected WMDs.
This leaves us guessing as to what the real reasons were for US involvement in Afghanistan, without which it is impossible to gauge whether the US achieved its goals or not.
My sense is the following: the US keeps getting into 'forever wars' not by accident, but because forever wars serve US interests. The US goal in Afghanistan and Iraq was a 'forever war' - continued conflict and instability.
Why would the US be interested in that?
Simple - the US is a maritime power that must dominate global trade and divide the Eurasian continent in order to maintain global dominance.
Being the most powerful maritime power and having strong maritime powers as its allies, domination of maritime trade is a given. However, the goal is to dominate global, and not just maritime trade.
As such, it is of prime strategic interest for the US to disrupt land-based trade routes to keep key rivals from establishing land-based alternatives to US-dominated sea routes.
The US lacks the means to efficiently invade and occupy large countries overseas, and therefore cannot seek hard, long-term control over vital trade regions. However, to disrupt trade hard control is not necessary - sowing chaos and instability is enough.
Enter the 'forever war': a (relatively) low-footprint, low-cost method of destabilizing key regions in the world for long periods of time.
The war in Afghanistan is a continuation of a long-standing US policy of sowing instability in Central Asia and the Middle-East that started with the overthrowing of the democratically elected government of Iran in 1953. The war successfully extended instability in the region for another 20 years.
When viewed through this lens, the war in Afghanistan was not a defeat at all.
So why is the US so interested in destabilizing this region? Because Central Asia and the Middle-East connect key US rivals: China, Russia and India (plus potential regional powers that may spring up in the Middle-East in the long-term like Iran, Saudi Arabia, Egypt and Turkey).
Note how this bloc of three countries comprises a gigantic portion of the world's population and natural resources.
To make a long story short, due to the nature of the wars the Americans fight, they often do not have to win decisive military victories in order to reach their goals. However, not winning a decisive victory is not the same as losing.