Does anyone here have an insight into how the Taliban might be going about taking towns and cities from the Afghan government (I expect Seff and other military folk might be able to shed some light on this for me)? What I am thinking of is where are the Taliban fighters physically coming from, and at what point do the government forces know they are nearby. Did the Taliban assemble in villages friendly to them before setting off towards their targets in a convoy of utes, or were many Taliban fighters living 'undercover' in the cities now falling to the Taliban, and taking up arms when told to do so by mobile phone etc. and taking defenders by surprise? When those Taliban fighters approaching from outside the town arrive, do they dismount and use small arms to suppress and snipe the government forces guarding roadblocks to begin advancing into the town? I am curious as to how it works.
One explanation is that mid to high levels of leadership are surrendering and allowing the Taliban through. It's one explanation that allows for this fast of an advance. Some of these agreements may have been negotiated long beforehand, but this is mostly speculation on my part.
But what about individual soldiers, small groups of soldiers, or maybe a few lieutenant level officer wanted to continue fighting? If communication were to be completely cutoff, even some conscripts will continue to fight and it might take some weeks for them to fold. Hope that other groups are fighting with you, and trying to reach the same objectives, and that command/punishment exists if they abandon their posts can keep some groups fighting. And in a place as large as Afghanistan such fighting would likely be a slog.
But getting orders from above that the leadership has negotiated a truce or surrendered and that the entire unit is standing down is going to stop almost all people from fighting. Particularly if amnesty is involved. What are you going to do? Fight alone against a cohesive and determined force by yourself? It's like spitting into the ocean. And once a chunk of the army has surrendered in this way, the pressure on the existing officers and commanders will increase leading to more defections.
Some more context though. Before the US entered Afghanistan the Taliban never had complete unitary control over the country. It existed like a feudal conglomerate where warlords controlled their holds and would come into conflict with one another from time to time. The year the US invaded was one such time. The Taliban were fighting a group of warlords - The Northern Alliance. It had some roots in the Whole 9/11 thing. The alliance mainly consisted of the minorities in that local area with their own group allegiance. Afghanistan neighbors Uzbekistan, Tajikistan, and Turkmenistan in the North, and the sizeable ethnic population spill overs in the North of Afghanistan were the main members of this alliance. Mainly Uzbeks and Tajiks though.
Traditionally he Taliban are mainly composed of Pashtuns, the countries biggest ethnic majority. This was true pre-invasion, almost all Pashtuns and few if any other minorities even among the lower levels. This time however, Uzbeks and Tajiks are in positions of power within the Taliban. The Uzbek commander who switched sides over to the Taliban was promoted as governor for one of the provinces for example as well as in the higher armed echelons. That being said, whether these are truly positions of power, if they are going to stay, or indeed, the Taliban may have truly softened some of their stances, only time can tell.
tldr; It looks like the American invasion has glued everyone together under the Taliban flag. Most of the senior officers and governors had some kind of deal to keep their power after the last foreign forces left, and the Kabul government never really had that much control over the rest of the country anyway and far off places were pretty much on their own to deal with the Taliban or warlords themselves even with the foreign troops around.