Answer: 1990.
Explanation:
While the United States had been increasingly stockpiling nuclear weapons since 1945, the Soviet Union only started the same process around 1965, and even strongly since 1975. Only by 1990, did the soviet union reach the 10,000 weapons mark that the US had already achieved in 1971. By the mid-1990s, both countries had begun to descend their stockpiles of strategic nuclear weapons.