//…the idea was to neutralise al-Qaeda in the country by removing the Taliban.
This was achieved.//
If that was the mission, it is no wonder it hasn’t worked.
Al Qaeda are quite different from the Taliban, with totally different aims.
Both had their origins in the mujahideen, the freedom fighters fighting the Russians after they invaded.
The mujahideen were made up of two components, Afghans who wanted their country back, and foreign Jihadists mainly from Saudi Arabia who wanted holy war.
When the Russians retreated, the mujahideen split.
Half became the Taliban who took over the country. The other half became al Qaeda who took their holy war ethos international, mainly against the United states.
Very quickly the two sides began to dislike each other. The Government in Kabul grudgingly tolerated Bin Laden’s men as long as they did their holy warring outside Afghanistan. At its peak, there were less than 400 al Qaeda operatives training in Afghanistan.
The United States regarded 9/11 as an act of war, and were going to avenge it with its military might. In the rush for war, they picked the wrong enemy. The Taliban could very easily have been bought for a fraction of what the war has cost. They would have given up al Qaeda at the drop of an hat. Instead, the US needed a war so they invaded. They easily toppled the Taliban and captured the country. After that, their efforts to nullify al Qaeda were unsuccessful.
So we’ve had a 20 year occupation of Afghanistan which gained us nothing. Terrorism was not defeated (increased if anything), and we have just given up the no-win game and left.
But to claim al Qaeda were neutralised by defeating the Taliban, and proclaiming that as achieving our mission, is
100% wrong.