Even as Japan marks the 78th anniversaries of the atomic bombings of Hiroshima and Nagasaki this week, the only country to experience the devastating effects of nuclear weapons in a conflict remains opposed to joining a treaty that aims to comprehensively prohibit and ultimately eliminate the world’s most destructive weapons.

Japan’s absence as a signatory to the United Nations’ Treaty on the Prohibition of Nuclear Weapons (TPNW) comes despite more than 90 nations having signed on to the pact, which prohibits states from developing, threatening to use or hosting other states' nuclear weapons on their territory.

Japan, which is positioned under the so-called nuclear umbrella of its top ally, the United States, has refrained from joining the treaty, citing its own “tough security environment.” Tokyo relies on American nuclear weapons to deter threats within the region, including China and North Korea’s own increasingly potent arsenals.