The nuclear arms race in the Cold War began shortly after World War II, with key developments occurring in 1949 when the Soviet Union tested its first atomic bomb. This event marked the onset of intense competition between the United States and the USSR to develop and stockpile nuclear weapons. The arms race was characterized by advancements in missile technology, the development of thermonuclear weapons, and strategies of deterrence. It heightened global tensions and led to a proliferation of nuclear arsenals, profoundly influencing international relations, military strategy, and global security policies throughout the latter half of the 20th century.