In 2008 I worked in the Konduz River Valley, known locally as the Valley of Four. The mayor, a former Taliban government minister, told me that the name (Chahar Darreh in Farsi) was a tribute to the four groups — Tajik, Uzbek, Turkomen, and Pashtun — that have lived together for decades in the valley, a floodplain dotted with mud-walled villages. The valley is isolated. To the west, a desert mountain range separates it from the thriving city of Mazar-e-Sharif. To the north, east, and south, the snake-like Konduz River cordons off the valley from Konduz City and the Ring...