These are the 9 nuclear-armed countries and the 31 allies they've vowed to defend with the world's most devastating weapons

A nuclear "triad" refers to a nation's ability to deploy its nuclear arsenal through intercontinental ballistic missiles, sea-launched ballistic missiles, and strategic bombers, as defined by the Nuclear Threat Initiative, an advisory board that conducts research and provides analysis to encourage diplomacy.

The US has agreed to potentially use its nuclear weapons to protect NATO member states, as well as Japan, Australia and South Korea.

Because of these agreements, all 29 NATO member states, and the three who hold bilateral protection agreements with the US, are in violation of TPNW.

The US, which has a nuclear arsenal that's nearly the size of Russia's, is the only nation in the western hemisphere that possesses nuclear weapons, and one of three countries to possess the nuclear "triad."

According to the Nuclear Weapons Ban Monitor, the US is believed to store some 180 nuclear weapons in other countries.

This number has been "significantly reduced since the Cold War," according to the report.

The United Kingdom is a NATO member state and shares in the umbrella protections of the alliance.

The kingdom maintains at least one nuclear-armed submarine on patrol at all times, under a Continuous at Sea Defense Posture, according to NWBM.

British policy also states that the country will not threaten the use of nuclear weapons against any "non-nuclear weapons state."

France, also a NATO member state, can only deliver its nuclear weapons via aircraft and submarines.

The ASMP-A is a 300 kiloton warhead, approximately 20 times the size of the bomb dropped on Hiroshima, Japan, at the end of World War II.

If a warhead of that size were to drop over Washington, DC, it would result in approximately 280,000 casualties.

China possesses a nuclear "triad," but has agreed not to employ nuclear weapons against any nation in a Nuclear Weapons-Free Zone, which include Latin American and Caribbean nations, as well as some in Africa, the South Pacific and Central Asia.

Although North Korean leader Kim Jong Un has publicly proclaimed a desire to denuclearize the entire Korean peninsula, there is no evidence that he has made any attempt to do so.

Reports vary as to the size of the North Korean nuclear arsenal. While the monitor follows conventional views that the country possesses 10 to 20 nukes, The Washington Post has previously reported that it may hold up to 60, citing confidential US assessments.

Israel has never publicly admitted to possession of nuclear weapons.

Nevertheless, the international community operates on the assumption that since its inception, Israel has developed and maintained a nuclear arsenal.

The size of Israel's cache remains unclear, and though it is possible that the nation holds enough enriched plutonium for 100 to 200 warheads, the NWBM accepts estimates from the Federation of American Scientists, which show that Israel possesses approximately 80 nuclear weapons.

Attempts to develop intercontinental and submarine-launched nuclear missiles indicate that India may soon possess the nuclear "triad."

Mainly due to tensions with Pakistan, some experts have questioned whether India's "no first-use" posture will endure.

Pakistan can deliver its nuclear weapons from the ground and air and is allegedly developing methods of sea-based delivery to complete the nuclear "triad."

Despite facing sanctions, Pakistan is reportedly expanding its nuclear arsenal faster than any other nation.

Similar to British policy, Pakistan claims it will not use or threaten to use its nuclear arsenal against any "non-nuclear" state, leaving many questions unanswered on the potential use against neighbor India, which also maintains nuclear weapons.