A civilian nuclear energy program has traditionally been the precursor to a country's ability to make a nuclear weapon. While it’s not the only route to weaponization, the technology used to manufacture reactor fuel (or, in case of plutonium, the waste product of some civilian nuclear reactors) can easily be repurposed for the creation of bomb materiel.

Many nations with civilian facilities that give them nuclear weapon capacity have nonetheless chosen not to build them. These nuclear threshold states remain under the scrutiny of International Atomic Energy Agency inspectors, but if they chose to break out of the Non-Proliferation Treaty — as North Korea did in 2003 — some could construct nuclear weapons in a matter of months. Japan is often cited as an example of a country that could very quickly build a nuclear arsenal should it decide to do so. Not every nuclear-armed state, however, also produces nuclear energy.

Looking at the location of nuclear-armed states in relation to one another, it’s clear that the decision to “go nuclear” is often prompted by neighbors or rivals acquiring the bomb.