In another context, I gave a back of the envelope calculation that WWII comprised approximately 1% of human history -- roughly 20 billion person-years were live

In another context, I gave a back of the envelope calculation that WWII comprised approximately 1% of human history -- roughly 20 billion person-years were lived during that time, and heavily influenced by it, compared to around 2.3 trillion person-years lived since anatomically modern humans first arose a couple-three hundred thousand years ago. Vietnam lasted longer, but only was a salient issue for a much smaller fraction of the world's population at the time, so probably less than a tenth of the person-years lived in the shadow of WWII were similarly affected by the Vietnam War. Unless there is a WWIII, the second World War will probably be the war of the human species, and a significant part of our history for centuries to come.