Castle Bravo was the worst U.S. nuclear accident, but many of its component problems—unpredictably large yields, changing weather patterns, unexpected fallout contamination of populations and the food supply—occurred during other atmospheric nuclear weapons tests by other countries as well. Concerns over worldwide fallout rates eventually led to the Partial Test Ban Treaty in 1963, which limited signatories to underground testing. Not all countries stopped atmospheric testing, but because the United States and the Soviet Union were responsible for roughly 86% of all nuclear tests, their compliance cut the overall level substantially. France continued atmospheric testing until 1974, and China until 1980.