In August 1945, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, bringing World War II to a close. Some 140,000 people died in the blasts, and many thousands died later from radiation sickness. The bombing of Hiroshima was the first use of atomic weapons, and the detonation set off a decades-long nuclear arms race between the former Soviet Union and the United States. The Cold War—as that arms race is called—cost both countries billions of dollars, created a global atmosphere of fear and mistrust, and eventually precipitated the collapse of the Soviet Union. With the dissolution of the Soviet Union in 1990, the Cold War ended, and so did much of the public's concern about nuclear weapons.

However, nuclear security is an even greater concern today than it was during the Cold War. The nuclear arms race during the Cold War...