Nuclear weapons have been in the news in recent months in a way they haven’t since the Cold War. North Korea has been testing a missile that could reach the continental United States. Both Trump and Russian president Vladimir Putin have signaled a renewed interest in increasing their respective nuclear arsenals, despite both countries having ratified the 1968 Nuclear Non-Proliferation Treaty. This Lowdown lesson will describe the history of nuclear proliferation as well as the science behind what makes nuclear weapons so deadly.