The Letter
In 1939, Albert Einstein and his fellow scientist colleagues had begun a project in nuclear fission, allowing them to create nuclear weaponry. Einstein penned a letter to Franklin Roosevelt warning him about the nuclear properties of Uranium, and that Germany was after the same element in order to use it as a nuclear weapon. Einstein wanted to tell Roosevelt to get a head start on the research. Little did Einstein know about the impact that this project was going to have.
After having received the letter from Einstein, Roosevelt takes the warning very seriously. A month later, Roosevelt assigns a research committee and later develops a nuclear program under the Army Corps of Engineers. On May 12, 1942, FDR signs the order of the confidential project of creating a nuclear bomb. The development of the nuclear bomb was the largest secret project the U.S. government had ever undertaken, so secret that not even Harry S. Truman, vice president during one of Roosevelt's terms, knew about the project. The project undertook the codename "Manhattan Project."
http://www.ushistory.org/us/51f.asp
http://www.ushistory.org/us/51f.asp
Though Einstein was the one who pushed Roosevelt to approve the research for the atomic fission, he wasn't the only one. On October 9, 1941, Vannaver Bush from MAUD committee, another committee dedicated for the research of the atomic bomb, went to visit Roosevelt and discuss nuclear fission, emphasizing on British findings and bomb costs, while also showing concern about the project and its impact. Roosevelt permitted Bush to explore and research construction needs, and advised him to work quickly, but to only work on developing research. Bush went to work, and before the bombing of the pearl harbor, Bush sent an undercover letter on November 27 to FDR about his findings. Bush informed FDR that the fission for Uranium-235 was feasible, and that the isotope separation would cost $50-100 million dollars. Roosevelt didn't respond until 3 months later, writing, "V. B. OK -- returned -- I think you had best keep this in your own safe FDR". After this, Bush went straight to work on overseeing engineering studies and supervising pilot plant construction.
Picture of a nuclear bomb
Manhattan Project
After Einsteins letters about Hitler looking for uranium to the make nuclear weapons, FDR started the Manhattan Project. FDR saw the letter as unimportant, but proceeded anyway. FDR's approval of the project had spurred the creation of various pilot plants, laboratories, and manufacturing facilities. President Roosevelt had left John Oppenheimer as one of the leaders in charge of the whole project, and later writes a letter to him telling him to move forward but with caution. Pretty soon the project received its code name, "The Manhattan Project." The Manhattan Project was a project on making an atomic bomb, it involved 120,000 Americans. It was hard to keep that many people quiet but only a few scientists and officials knew about the development. To show how well kept this secret was President Truman only found out after he was elected President of the United States. The bomb cost 2 billion dollars. Early in the morning on July 16, 1945 the first atomic bomb was tested just south of Albuquerque, New Mexico. The results were better than anyone imagined. A blinding flash visible for 200 miles lit up the morning sky. A mushroom cloud reached 40,000 feet, blowing out windows of civilian homes up to 100 miles away. When the cloud returned to earth it created a half-mile wide crater metamorphosing sand into glass(ushistory.org). The people who tested the bomb had to come up with a bogus story to conceal the truth.
Japan
The US dropped a bomb on Nagasaki, Japan in August of 1945. One day Japan dropped bombs on Hiroshima and Nagasaki. The bombing took an estimated of 200,000 lives. The people who survived the exposure to the bomb's radiation lived shorter than others but it wasn't too severe, but the exposure to the brought increased risks to cancer. The children of the parents who survived were predisposed to genetic diseases.
Without the Manhattan Project none of this would have been possible. There are two ways to look at this, A the US stopped WWII or B, because of the Manhattan Project the US caused a huge amount of damage through nuclear warfare. FDR stood up for the right thing and his choice by going through with the Manhattan Project was huge. This brought the world into a nuclear age and can be devastating to everyone. Since nuclear weapons are still fairly new there is only about 15,350 warheads. The Earth is not at risk to be blown up because there needs to be a lot more that 15,350 warheads to do it.