We live in dark times.
The Doomsday Clock is at two minutes to midnight, meaning we could easily see the end of the world as we know it.
World War 3 fiction has been on the go pretty steadily since the end of World War II. The conflicts that have arisen since then, while devastating, have not been anywhere near as scary and apocalyptic as the second World War. Meaning WW3 would likely top it and destroy us all.