Trump wants to test nuclear weapons. Here's why we stopped

In 1963, the U.S., the United Kingdom and the Soviet Union signed the Partial Nuclear Test Ban Treaty to stop nuclear tests in the atmosphere, outer space and underwater.

The decision was made over environmental concerns and the fallout of the Cuban Missile Crisis, per the CSIS. The Threshold Test Ban Treaty in 1974 limited the yield of underground testing to below 150 kilotons. In 1992, Congress passed a resolution that prohibited the U.S. from conducting underground nuclear tests unless a foreign state did so, leading to the current moratorium. Of note: The 1997 Comprehensive Test Ban Treaty sought to ban all nuclear testing worldwide, and it proved largely successful even though it was not universally ratified.