We never learn:

Grenades made in the United States and sent to Central America during the Cold War have resurfaced as terrifying new weapons in almost weekly attacks by Mexican drug cartels.

Sent a generation ago to battle communist revolutionaries in the jungles of Central America, U.S. grenades are being diverted from dusty old armories and sold to criminal mafias, who are using them to destabilize the Mexican government and terrorize civilians, according to U.S. and Mexican law enforcement officials.

The redeployment of U.S.-made grenades by Mexican drug lords underscores the increasingly intertwined nature of the conflict, as President Felipe Calderón sends his soldiers out to confront gangs armed with a deadly combination of brand-new military-style assault rifles purchased in the United States and munitions left over from the Cold War.