On August 6th, 1945, the first nuclear weapon to be used in warfare, "Little Boy," exploded above Hiroshima at an altitude of 1,800 ft. By 1950, 230,000 people had died from injuries or radiation caused by the explosion.
Between October 14th, 1962 and November 20th, 1962 the Cold War almost turned into a full-scale nuclear war. The Cuban Missile Crisis, as it came to be called, ended with the USSR's withdrawal of nuclear missiles from Cuba. The human race has never come closer to extinction.
Today, rough estimates put the number of nuclear weapons worldwide between 30,000 and 40,000. The human race has been walking a tight rope since the end of World War II, it is only a matter of time until he falls off, and the results will be unimaginable.