Manhattan Project

In 1939, German Scientists began developing Nuclear Research and learning the secrets to splitting a Uranium atom. Fear began to spread through Europe of the idea that Germany might have the power of mass destruction. In 1941, with the urge of Albert Einstein, the Manhattan Project was created. It's only objective to create and design an Atomic Bomb. With leading Scientists from many countries, Los Alamos in New Mexico was allocated for the building of the bomb. Since keeping the building of the Atomic Bomb a secret was a priority, Churchill and Roosevelt mutually agreed to not leak any information to anyone including Stalin. In July of 1946, the first Atomic bomb was ready to be tested. The blast of the first test was so strong that it blew down houses 100 miles away from the drop site. The drop created a mushroom cloud reaching 40,000 feet in the air, this shocked scientists who were not prepared to witness the massive destructive power of their creation. A story was made up and covered up the real facts of the drop site, word was sent to President Truman while he was in Germany, and set the world into a Nuclear Phase. President Truman at Potsdam, Germany, brought to attention the new power that the US had. Stalin, who was not informed officially, had spies on the Manhattan Project. Stalin had his spies including Klaus Fuchs, Theodore Hall, David Greenglass, Harry Gold, Julius and Ethel Rosenberg supply the Soviet Union with information and detailed reports on how to build the Hydrogen Bomb. Soon after the Potsdam Conference, Truman authorized the dropping of two bombs on Japanese cities, Hiroshima and Nagasaki. The world was in shock as something so powerful was able to demolish those cities.

http://www.ushistory.org/us/51f.asp
http://www.atomcentral.com/the-cold-war.aspx