Which event marked the start of the nuclear arms race

The deployment of the atomic bombs in the cities of Hiroshima and Nagasaki on August 6 and 9 of 1945 were the events that would eventually bring the Second World War to an end, as the Japanese empire would sign its surrender to the Allies in 1945.

This was the opening event in the nuclear arms race that would continue throughout the Cold War between the United States and the Soviet Union. A period of time that would last since the end of World War 2 until the collapse of the Soviet Union in 1991.