The United States conducted the world’s first successful nuclear weapons test in July 1945. Four years later, the Soviet Union tested their first nuclear weapon. These tests triggered a decades-long arms race between the two superpowers.

Between 1945 and 1996, more than 2,000 nuclear tests were carried out — 1,032 of them by the United States and 715 of them by the Soviet Union, according to the UN. Britain carried out 45 tests, France 210 and China 45.

The radioactive fallout from those tests drew criticism from around the globe. The international community’s concern about the effects on health and the environment continued to grow. As a result, several attempts to curb the explosive tests were made.

Must read: Comprehensive Nuclear Test Ban Treaty (CTBT) – signatories and legal status

The 1963 Limited Nuclear Test-Ban Treaty (LTBT) was one of the first such attempts. It prohibited nuclear testing in the atmosphere, outer space, and underwater, but underground tests were still permitted.

To tackle the limitations of LTBT, a comprehensive test ban was discussed during the negotiation of the Nuclear Nonproliferation Treaty in 1968. However, no agreement was reached on the issue.

Six years later, the US and Soviet Union agreed to sign the Threshold Test Ban Treaty (TTBT), which established a nuclear “threshold” by banning the two countries from conducting tests that would produce a yield exceeding 150 kilotons (equivalent to 150,000 tons of TNT).

Must read: Nuclear non-proliferation treaty

The mutual restraint imposed by the Treaty reduced the explosive force of new nuclear warheads and bombs, which could otherwise be tested for weapons systems. The TTBT was not intended as a substitute for a comprehensive test ban.

A major breakthrough only came after the Cold War ended around 1990 and the disintegration of the Soviet Union. As the geopolitical tensions simmered down, the UN took advantage of the situation and adopted the CTBT, which put a blanket ban on the explosive testing of nuclear weapons, on September 10, 1996, and it opened for signature on September 24, 1996.