It began with individual outposts in rural areas where starving and ammunition-depleted soldiers and police units were surrounded by Taliban fighters and promised safe passage if they surrendered and left behind their equipment, slowly giving the insurgents more and more control of roads, then entire districts. As positions collapsed, the complaint was almost always the same: There was no air support or they had run out of supplies and food.

But even before that, the systemic weaknesses of the Afghan security forces — which on paper numbered somewhere around 300,000 people, but in recent days have totaled around just one-sixth of that, according to U.S. officials — were apparent. These shortfalls can be traced to numerous issues that sprung from the West’s insistence on building a fully modern military with all the logistical and supply complexities one requires, and which has proved unsustainable without the United States and its NATO allies.

Soldiers and policemen have expressed ever-deeper resentment of the Afghan leadership. Officials often turned a blind eye to what was happening knowing full well that the Afghan forces’ real manpower count was far lower than what was on the books, skewed by corruption and secrecy that they quietly accepted.