In 1949, Soviet Union detonated its first atom bomb, ending U.S. monopoly on atomic weapons, more than seven decades later United States and Russia together hold over 80 per cent of world's nuclear arms stockpile

On August 29, 1949, the Soviet Union conducted its first successful atomic bomb test, marking a decisive turning point in the history of the nuclear age. The test, conducted at the Semipalatinsk test site in what is now Kazakhstan, ended the United States’ brief monopoly on atomic weapons. The United States had been the only nation to possess nuclear weapons since the 1945 atomic bombings of Hiroshima and Nagasaki. When Washington confirmed evidence of the Soviet explosion in September 1949, the development dramatically altered the strategic balance between the two emerging Cold War superpowers.

The first Soviet device was known as RDS-1 in the Soviet Union and was sometimes called “First Lightning” in later accounts. Its successful detonation surprised American policymakers because the United States had expected the Soviet program to take longer. The discovery was initially made through scientific and intelligence monitoring rather than a Soviet announcement. On September 23, 1949, President Harry S. Truman publicly stated that the United States had evidence of an atomic explosion in the Soviet Union. Soviet officials subsequently confirmed possession of atomic weapons.