There are currently nine countries in the world with nuclear weapons, including the UK, China, France, the United States and Russia.
These five nations are officially recognised as possessing nuclear arms by the Nuclear Nonproliferation Treaty (NPT) - with the US and Russia holding the vast majority between them.
But there are also four other countries that have the devastating weapons but hold them illegally.
These are India, Pakistan, Israel and North Korea.
The first nuclear weapons were developed by the US during World War Two as part of the Manhattan Project in reaction to the Nazi threat in Germany.
America received cooperation from the UK and Canada.
The latest nation to build nuclear weapons is North Korea, which carried out its first nuclear test in 2006.
It has since threatened nuclear action against the US and South Korea, and has broken international law with its testing of powerful nuclear weapons.
There were thought to be 13,865 nuclear warheads in 2019, down from 14,465 in 2018.
The statistics used in this piece come from the 2019 report from the Stockholm International Peace Research Institute.
The institute notes that ‘deployed warheads’ are those placed on missiles or located on bases with operational forces.
Other warheads relate to those which have been stored or reserve warheads and retired warheads awaiting dismantlement.
All estimates are approximate and figures for North Korea are uncertain and therefore not included in total figures.