Cold war tensions were underpinned by the fear of nuclear war nuclear weapons derive their energy from nuclear reactions called fission or fusion they are capable of enormous destructive power thousands of times greater than conventional explosives the detonation of some nuclear weapons is capable of destroying an entire city. The end of wwii when the us soviet union and their other allies began to build an abundance of nuclear weapons beginning in wwii the first nuclear weapon was built by the us and to be used on nazi germany and its allies shortly after joseph stalin was initially. The role that the invention of nuclear weapons played in bringing world war ii to an end remains debatable but the fact is undeniable that these powerful new weapons drastically changed the nature and potential intensity of modern warfare thankfully as of january 2014 no nuclear weapons have been employed in combat since august 1945. The history of cold war nuclear weapons dates back to world war ii when the united states dropped two nuclear bombs on japan while these were the only two nuclear bombs to be used during active warfare their use spawned a nuclear arms race that lasted for more than half a century