In the 1930s, Hitler's Germany became the most powerful—and feared—country in Europe. Hitler was determined to control the entire continent. After the shocking attack on Pearl Harbor, the United States declared war on Japan. In turn, Germany declared war on America, igniting World War II. The biggest concern for America and the Allies was that Hitler was working on a nuclear "super bomb." Believing the fate of the world hung in the balance, President Franklin Roosevelt approved a top secret project known as the Manhattan Project to create the first atomic weapon. In a race against the clock and under the direction of J. Robert Oppenheimer, scientists from all over the world working at the Los Alamos Laboratory in New Mexico spent four years developing what would become the world's deadliest weapon. The decision to use the bomb on Japanese citizens ended World War II but began a controversy that rages to this day.