Nuclear bombs are catastrophic weapons of mass destruction that have the power to wipe out entire cities and kill hundreds of thousands of people in an instant. When were these weapons first developed? Such bombs generate their huge explosive power through the splitting—or fission—of certain elements, such as uranium or plutonium. While nuclear powers such as the United States and the Soviet Union/Russia have conducted more than 2,000 tests of these weapons to date, they have been used in warfare just twice. Toward the end of World War II, the U.S. dropped two atomic bombs on the Japanese cities of...