The first atomic bomb, developed by the Manhattan Project during World War II, was tested on July 16, 1945, at the so-called Trinity site in the New Mexico desert. As with all such weapons, the bomb’s destructive effects included not only the actual blast—the most powerful known at the time—but also blinding light, intense heat, and deadly radioactive fallout. An atomic bomb was first used in warfare on August 6, 1945, when the United States dropped one on Hiroshima, Japan; a second bomb was dropped on Nagasaki three days later. After the war, the United States conducted additional atomic tests in the Pacific and in Nevada. In 1949 the Soviet Union conducted its first atomic bomb test, causing leaders in the United States and elsewhere to begin to think about the international control of atomic weapons. At the same time, the Soviet explosion led to a nuclear arms race between the United States and the Soviet Union—a race that would last for several decades, despite eventual test bans and additional restrictions.

The first atomic bomb, developed by the Manhattan Project during World War II, was tested on July 16, 1945, at the so-called Trinity site in the New Mexico desert. As with all such weapons, the bomb’s destructive effects included not only the actual blast—the most powerful known at the time—but also blinding light, intense heat, and deadly radioactive fallout. An atomic bomb was first used in warfare on August 6, 1945, when the United States dropped one on Hiroshima, Japan; a second bomb was dropped on Nagasaki three days later. After the war, the United States conducted additional atomic tests in the Pacific and in Nevada. In 1949 the Soviet Union conducted its first atomic bomb test, causing leaders in the United States and elsewhere to begin to think about the international control of atomic weapons. At the same time, the Soviet explosion led to a nuclear arms race between the United States and the Soviet Union—a race that would last for several decades, despite eventual test bans and additional restrictions.