The surrenders seem to be happening as fast as the Taliban can travel.

In the past several days, Afghan security forces have collapsed in more than 15 cities under the pressure of a Taliban advance that began in May. On Friday, officials confirmed that those included two of the country’s most important provincial capitals: Kandahar and Herat.

The swift offensive has resulted in mass surrenders, captured helicopters and millions of dollars of U.S.-supplied equipment paraded by the Taliban on grainy cellphone videos. In some cities, heavy fighting had been under way for weeks on their outskirts, but the Taliban ultimately overtook their defensive lines and then walked in with little or no resistance.