Can history teach us what happens next? Almost eight decades after J Robert Oppenheimer built the first atom bombs, the threat of nuclear annihilation seems real once again.
Russia threatens nuclear strike as Moscow hit
Bombastic: The nuclear threats come after Ukraine launched drones into the heart of Moscow. Glossary
Hiroshima - A Japanese city destroyed by an atomic bomb in World War II.
Nagasaki - A city in Japan that was hit by an atomic bomb during World War Two.
Radiation sickness - Damage caused to the body after it receives a high dose of radiation in a short amount of time. It can be life-threatening.
Tactical nuclear weapons - Nuclear weapons that are meant to be used to make small gains on the battlefields, rather than to destroy whole cities.
Dmitry Medvedev - A Russian politician and former president and prime minister.
John F Kennedy - President of the US from 1961 to 1963, when he was shot dead in Dallas. He was the fourth American president to be assassinated; Abraham Lincoln was the first.