Short Term Impact
Under Oppenheimer's leadership, three bombs had been developed and two were used in ending World War II. On August 6, 1945 the United States detonated the first atomic bomb on Hiroshima. Estimates run between 90,000 and 150,000 killed at Hiroshima and 40,000 to 80,000 at Nagasaki. An immediate short term impact was the shortening of a war that could have lasted much longer with millions of more dead on both sides.
Another short term impact was the immediate question of who would control the atomic weapons, how many would be made, and if new, more deadly types of atomic weapons would be developed. Oppenheimer protested the development of the much more deadly hydrogen bomb. This controversy continued for a few years after World War II.
The Soviet Union, once the United States' ally, used espionage to gain the technology to develop their own atomic bomb. Oppenheimer was questioned about his possible participation in the espionage.
Long Term Legacy
As Oppenheimer stated, the atomic bomb he had helped developed 'had become death.' Even though Oppenheimer opposed the making of stronger and larger bombs, the United States, Soviet Union, and other countries continued the nuclear arms race. Oppenheimer's desire for international control of nuclear weapons and powers failed. The development of nuclear weapons such as the hydrogen bomb led to many more countries having nuclear weapons, others seeking to develop them, and finally the opportunity for terrorists and other groups to utilize them in attacks against nations.
Oppenheimer became the symbol for the Red Scare and accused of being a communist. Although never proven to be a security risk or a member of the Communist Party, Oppenheimer was denied access to top security studies.
Oppenheimer's legacy is a controversial one. After World War II, Oppenheimer was widely admired as the "Father of the Atomic Bomb" while the bomb itself was greatly feared. His actions early in his career with friends and family who were known Communists clouded others view whether he was a true American or a security risk. Controversy continued to surrounded Oppenheimer as the world entered the atomic age. His brilliance as a scientist and ultimately as a leader became tainted behind these controversies.
(Interview with Robert Oppenheimer BBC)