On the date of August 2, 1939, about 6 months before the actual start of WWII, Albert Einstein wrote a letter to the President of the United States. The letter said that the Nazis in Germany were planning to purify, or clean, uranium-235, or the liquid used in present day atomic bombs. Shortly after the letter, the United States started a project called the "Manhattan Project." This was a project that would create the weapon of mass destruction called the Atomic Bomb.