The final report from a government watchdog tasked with overseeing Afghanistan reconstruction efforts reveals impact of weapons and equipment left behind.

The U.S. invaded Afghanistan on October 7, 2001, in response to the 9/11 attacks a month earlier. The U.S. presence in Afghanistan then continued under four presidents.

Taliban officials admit that at least half of the stockpile is now “unaccounted for.” Many of those weapons ended up with ...