Also in 1947, under the National Security Act, the armed services were put under the authority of the newly created National Military Establishment (NME), to be headed by the secretary of defense. In 1949 the National Security Act was amended, and the NME was transformed into an executive department--the Department of Defense. The Armed Forces Special Weapons Project, which would coordinate the Defense Department's responsibilities in the area of nuclear weapons, became the military heir to the Manhattan Engineer District. The Military Liaison Committee was also established as an intermediary between the Atomic Energy Commission and the Defense Department; it was also to help set military requirements for the number and type of nuclear weapons needed by the armed services.
The war between Germany and most of the rest of Europe came in a series of challenges that began as soon as Hitler came to power in Germany in 1933. Under Hitler’s leadership, Germany broke out from the isolation the other European countries had tried to impose with the Versailles Treaty. The Fuhrer created a Nazi Germany whereby he was poised to conquer and control all of Europe, focusing his vengeance out on those who signed against him in the Treaty of Versailles . He ignited the torch of war in 1939 when he sent his armies into Poland, starting a conflict that would spread warfare from the capitals of Europe to the sands of North Africa, and the Far East. While Europe saw its destruction during the subsequent years after the Polish invasion, America, up until its declaration of war on Japan in December 1941, had remained overwhelmingly isolationist, with the US Congress determined to avoid entanglements abroad. There were also isolationist forces that felt the Allies would win the war in the end anyway, that America was not directly threatened from German advances, and that an Axis victory would not menace US security. What led the United States into the Second World War was a combination of the following: