Thursday marked the anniversary of the bombing of Hiroshima, which hastened the end of World War II. Global superpowers spent the decades after the bombing of Hiroshima building up stockpiles of nuclear weapons, and then a few more decades after that trying to reduce those stockpiles. Today, we look at that historic arms race, and the new nuclear rivalries between the US, Russia and China. Laicie Heeley from the podcast Things That Go Boom has our special report.