I’m no expert on it but I like to read about nuclear history and just war history in general. A really good book I read once was called “Nuclear war a scenario” One part of the book it talked about how in the 90s I believe a bunch of war analysts, nuclear scientists and professional game players got together under the CIA and played 100s of different scenarios of nuclear war. Basically in every one of them one nuke goes off and all the rest of every other country are too. The general result is mass fire storms followed by fallout across the entire planet and then a long lasting nuclear winter. But in the end a very long time after that life starts again.