Nuclear powers

In our world, nations known as the nuclear powers (sometimes called "Nuclear Weapon States"), are those countries which are known to openly possess stockpiles of tactical and strategic nuclear weapons. There are currently only five nation-states on Earth that are recognized as controlling large stockpiles of nuclear weapons while still being in compliance with the demands of the Nuclear Non-Proliferation Treaty of 1968. These five nations are the United States, the United Kingdom, France, Russia and China, who also happen to be the five permanent members of the United Nations Security Council and hold vetoes over the decisions of that body. Only four recognized sovereign states on the planet are not parties to the treaty: India, Israel, Pakistan and North Korea. India, Pakistan and North Korea have openly tested nuclear weapons and declared that they possess such weapons. Israel has had a policy of opacity regarding its own nuclear weapons program. North Korea at first acceded to the treaty, then violated it by producing both fissionable weapons-grade uranium and plutonium to build several atomic bombs, and then withdrew from it in 2003 rather than allow international inspectors to enter the country and inspect its nuclear material processing facilities.

Fallout universe
As all of the Fallout games take place in an alternate universe that diverged from our own after the end of World War II and as early as 1947, it is unknown how many and which states of the world in that universe had access to nuclear weaponry or if any nuclear treaties were ever signed. Given the available information on pre-Great War countries in the Fallout universe, it is fairly obvious that both the United States and China possessed them, though they were likely nuclear bombs and nuclear-tipped ballistic missiles that possessed much lower explosive yields and much higher amounts of radioactive fallout than the weapons currently in those nations' arsenals in our own reality. The Soviet Union, which survived long into the twenty-first century in the Fallout universe and did not collapse in 1991 as in our world, is implied to also have possessed nuclear weapons, and during the Resource Wars that began in 2052, the European Commonwealth and the oil-rich nations of the Middle East both suffered from a limited but mutual nuclear exchange. It is known that terrorists have also been able to gain access to nuclear weapons, as per the terrorist strike that destroyed Tel Aviv, Israel with a nuclear weapon in December 2053.