The Great War was a nuclear exchange between the countries of world, and is a term used by the inhabitants of post-apocalyptic America. It is one of the most, if not the most important event in the Fallout Universe and Series. It began on October 23, 2077, and ended a couple of hours later. The world and it's people endured more suffering in those hours than all of the other wars on the Earth combined.
 Leading up to the War
The Great War didn't just happen out of the blue, it slowly escalated from a minor problem to a world-wide disaster. Tension between countries and states and the lack of fossil fuels was a big part of it, a long with wars such as the United States and China and the European Commonwealth and other Nations.