The Soviet Union exploded a nuclear device in 1949. It was similar to “Fat Man” and was built using information delivered to that country by spies. China, Britain, and France developed nuclear weapons in the 1950s.

South Africa had nuclear weapons but abandoned the program. Israel is suspected of having weapons, but has never admitted it. India and Pakistan have both tested nuclear weapons. Iran and North Korea are suspected of developing nuclear weapons.

By 1953 there had been 50 above-ground tests of nuclear weapons that created radioactive fall-out, contaminating milk and animals. These effects alerted the public to the danger of such testing. The Cold War, however, created an atmosphere in which treaties could not be negotiated. In 1963 a partial test ban treaty was signed, prohibiting tests in the atmosphere, underwater, and in space. In 1968 the nuclear non-proliferation treaty was signed. Non-nuclear weapon states were prohibited from building or acquiring nuclear weapons. Many nations have signed the treaty, although some major states did not on the basis that it makes no effort to curb development by states that already have such weapons. In 1996 the comprehensive test-ban treaty was adopted by over two-thirds of the members of the United Nations general assembly. The United States has signed but rejected ratification in 1999. Nevertheless, 337 facilities around the world monitor compliance with the treaty. They send data to a center in Vienna for analysis and distribution to the states that have signed the treaty.