The cold war effectively ended at the Berlin Wall when it fell in 1989-90. It effectively began in 1942 at PO Box 1663 in Santa Fe. This was the address for Los Alamos when it was a secret city during World War II.
On December 28, 1942, President Roosevelt authorized the formation of the Manhattan Project to combine the various research efforts with the goal of weaponizing nuclear energy. Facilities were set up at Los Alamos, Tennessee, and Washington, as well as sites in Canada, for this research and related atomic tests to be performed.
The controversial creation and eventual use of the atomic bomb engaged some of the world’s leading scientific minds, as well as the U.S. military—and most of the work was done at Los Alamos. The Manhattan Project was started in response to fears that German scientists had been working on a weapon using nuclear technology since the 1930s—and that Adolf Hitler was prepared to use it.
Theoretical physicist J. Robert Oppenheimer was already working on the concept of nuclear fission (along with Edward Teller and others) when he was named director of the Los Alamos Laboratory in 1943.
Scientists working under Oppenheimer had developed two distinct types of bombs: a uranium-based design called “the Little Boy” and a plutonium-based weapon called “the Fat Man.” With both designs in the works at Los Alamos, they became an important part of U.S. strategy aimed at bringing an end to World War II.
On July 16, 1945, at the Trinity Site, just south of present day US 380, the first atomic bomb was successfully detonated creating an enormous mushroom cloud some 40,000 feet high. This controversial and monumental event in human history ushered in the Atomic Age. The Cold War began and dominated world politics for almost 50 years.
Upon witnessing the world's first nuclear explosion, Dr. Oppenheimer recalled a quote from the Hindu sacred text the Bhagavad-Gita:
"Now I am become Death, the destroyer of worlds".