Why did the U. S. and Soviet Union agree to stop detonating bombs in 1963?

Nuclear Test-Ban Treaty, formally Treaty Banning Nuclear Weapons Tests in the Atmosphere, in Outer Space, and Under Water, treaty signed in Moscow on August 5, 1963, by the United States, the Soviet Union, and the United Kingdom that banned all tests of nuclear weapons except those conducted underground.

Explanation:

health and medicine because people are dying from not being healthy or not strong enough medicine