The world is officially 'free' of chemical weapons. Here's what that means
The U.S. has destroyed the last of its stockpile of sarin nerve agent, fulfilling a decades-old obligation.
(Image credit: David Zalubowski/AP)

The U.S. has destroyed the last of its stockpile of sarin nerve agent, fulfilling a decades-old obligation.
(Image credit: David Zalubowski/AP)