I was working on a Cold War project for school, and was wondering if the American development of the atomic bomb was the first attempt at creating a nuclear weapon. Were there any other organizations or individual scientists researching nuclear weaponry and the creation of a nuclear bomb before WWII, or was the Manhattan Project the first true research into the creation of a nuclear bomb?
The Manhattan Project was the first full-scale program to develop nuclear weapons. There were several other research-scale programs during World War II that started between 1939-1941, by the United States, United Kingdom, Germany, Japan, the Soviet Union, and France. The goals of these were not bomb production, but attempting to figure out whether bombs could be made. The US research program started in 1939 but did not become a production program until 1942.
The scientific ideas behind the atomic bomb were public knowledge by 1939. But actually building a nuclear weapon requires a massive investment. All countries but the US and UK decided that the investment was too risky/difficult during wartime. The UK thought it was too large for them to undertake but persuaded the US to do it. (Even the US was surprised at how difficult it was — it cost much more than they expected and took longer than they thought.)