This is one of the few times I will use my status as a veteran to give me a little credibility to speak on a topic. Granted my service ended just as our engagement in Afghanistan began, but I did serve, and I studied the region during the later years of my career.
After over 20 years, we were no closer to defeating the Taliban than we were on day one. Like the Russians, we continued to fight a conventional war with a non-conventional enemy and in the end, the Afghan Mujahideen ran the Russians out and the Taliban simply waited us out! Without major cultural changes or the US adapting a "total war" mentality (neither of which were likely), we could have stayed 20 more years and the minute we left, what happened would have happened anyway. Yes, there were some serious miscalculations on how well the Afghan military would fight to defend their own country from the enemy within, but much like South Vietnam, we could only prop them up so much. At some point they would have to decide on their own if they were willing to fight or not, and we see what road they took. They were never fully committed to fighting the Taliban on their own and pretty much gave up with the little to no fight at all. It was our fight all along!
In no way shape or form do I mean any disrespect to my fellow veterans or current men and women who served in Afghanistan, I know all served with honor and pride. But as military members we have to understand that the military is but one of the instruments of national power that our government can use to resolve conflict, and its role is limited if not fully integrated with the other instruments to include diplomacy, economy, and information. While it will be debated and studied for years to come, if the goal was to destroy and keep terrorist groups (al-Qaeda and others) from using Afghanistan as a base of operations, I'm not sure if we will ever figure out if we used the other instruments of national power appropriately to help achieve our goals in Afghanistan. Our military had the lead and was put in an unfortunate situation that proved to be a bridge to far! To their credit, they devised plans and conducted operations that if nothing else kept the Taliban at bay and severely hampered terrorist group operations, but it must be clearly understood; at no time were we winning the war in Afghanistan. It's sad but true that most Americans were not even aware we were still fighting in Afghanistan! The US presence and military operations in Afghanistan were not sustainable and our departure and the Taliban take over was probably inevitable. The chaotic scenes we have been seeing and reading about show a lack of planning and poor execution if there was a plan. Shame on US if there was not a fully vetted exit plan that outlined every aspect of an orderly departure--we had 20 years to work on it!
The chaff and chatter of the blame game for the failures in Afghanistan will go on for months and years to come (and there is plenty of blame to go around). But we are where we are and all this means is that going forward, we will have to be even more vigilant in staying ahead of the terrorist threat from players who will now see Afghanistan as a launching pad to plan and conduct attacks against US. We'll just have to deal with that reality and use other means to preemptively detect, infiltrate, and destroy these elements before they reach our shores.