Nuclear testing: Why did it stop, why test and who has nuclear weapons?

A mushroom cloud rises with ships below during Operation Crossroads nuclear weapons test on Bikini Atoll, Marshall Islands in this 1946 handout provided by the U.S. Library of Congress. The United States said on April 25, 2014, it was examining lawsuits filed by the Marshall Islands against it and eight other nuclear-armed countries that accuse them of failing in their obligation to negotiate nuclear disarmament. REUTERS/U.S. Library of Congress/Handout via Reuters/File Photo