forget about world war 3, instead envision global war 1. it will be very superficially similar to the great war, in that men will be transported by trains, trucks, and ships and ordered by incompetent commanders to use outdated tactics against new weapons to try and conquer a worthless no man's land. nuclear weapons will not be deployed because no nuclear powers will be threatened. it will be presented as a regrettable necessity due to the various defense treaties signed by different nations, just the sort of thing you'd expect from our "clueless" fumbling overlords. any able-bodied young man will be harassed by law enforcement to enlist, and most food and material will be reserved for the war effort anyway, so to a lot of people enlistment will seem like the sensible option. but enlistment will most likely mean death, most recruits will be loaded onto troop carriers and then sunk by torpedoes just a few miles off shore. no telling what you will need to do to survive, but if you can find a position in the backlines be advised that asking a lot of questions will almost certainly get you sent to "combat."
United States