China tested its first nuclear weapon device in 1964 ("596") at the Lop Nur test site. The weapon was developed as a deterrent against both the United States and the Soviet Union. China would manage to develop a fission bomb capable of being put onto a nuclear missile only two years after its first detonation. It tested its first hydrogen bomb in 1967 ("Test No. 6"), a mere 32 months after testing its first nuclear weapon (the shortest fission-to-fusion development known in history). The country is currently thought to have had a stockpile of around 240 warheads, though because of the limited information available, estimates range from 100 to 400. China is the only nuclear weapons state to give an unqualified negative security assurance to non-nuclear weapon states and the only one to adopt a "no first use" policy.

India is not a member of the Nuclear Non-Proliferation Treaty. India tested what it called a "peaceful nuclear explosive" in 1974 (which became known as "Smiling Buddha"). The test was the first test developed after the creation of the NPT, and created new questions about how civilian nuclear technology could be diverted secretly to weapons purposes (dual-use technology). India's secret development caused great concern and anger particularly from nations that had supplied it nuclear reactors for peaceful and power generating needs such as Canada. It appears to have been primarily motivated as a general deterrent, as well as an attempt to project India as regional power. India later tested weaponized nuclear warheads in 1998 ("Operation Shakti"), including a thermonuclear device.

Pakistan is not a member of the Nuclear Non-Proliferation Treaty either. Pakistan covertly developed nuclear weapons over many decades, beginning in the late 1970s. Pakistan first delved into nuclear power after the establishment of its first nuclear power plant near Karachi with equipment and materials supplied mainly by western nations in the early 1970s. Pakistani Prime Minister Zulfiqar Ali Bhutto promised in 1965 that if India built nuclear weapons Pakistan would too, "even if we have to eat grass." The United States continued to certify that Pakistan did not possess nuclear weapons until 1990, when sanctions were imposed under the Pressler Amendment, requiring a cutoff of U.S. economic and military assistance to Pakistan. In 1998, Pakistan conducted its first six nuclear tests at the Chagai Hills, in response to the five tests conducted by India a few weeks before. Over the years, Pakistan has developed into a crucial nuclear power. It's also alleged that Pakistan is still drastically increasing its nuclear stockpile.

  North Korea was a member of the Nuclear Non-Proliferation Treaty, but announced a withdrawal on January 10, 2003 after the United States accused it of having a secret uranium enrichment program and cut off energy assistance under the 1994 Agreed Framework. In February 2005 they claimed to possess functional nuclear weapons, though their lack of a test at the time led many experts to doubt the claim. However, in October 2006, North Korea stated that due to growing intimidation by the USA, it would conduct a nuclear test to confirm its nuclear status. North Korea reported a successful nuclear test on October 9, 2006 (see 2006 North Korean nuclear test). Most U.S. intelligence officials believe that North Korea did, in fact, test a nuclear device due to radioactive isotopes detected by U.S. aircraft; however, most agree that the test was probably only partially successful. The yield may have been less than a kiloton, which is much smaller than the first successful tests of other powers; however, boosted fission weapons may have an unboosted yield in this range, which is sufficient to start deuterium-tritium fusion in the boost gas at the center; the fast neutrons from fusion then ensure a full fission yield. North Korea conducted a second, higher yield test on May 25, 2009

  Israel is not a member of the Nuclear Non-Proliferation Treaty and refuses to officially confirm or deny having a nuclear arsenal, or having developed nuclear weapons, or even having a nuclear weapons program. Israel has pledged not to be the first country to introduce nuclear weapons into the region, but is also pursuing a policy of strategic ambiguity with regard to their possession. Israel may have tested a nuclear weapon along with South Africa in 1979, but this has never been confirmed