China invades Taiwan and the US helps defend them.
China’s president Xi Jingping’s remarks about taking Taiwan back over during his address to the nation this year.
I work with someone who is currently high ranking in a corporation and is a retired submariner who was also in intelligence and is currently in the reserves. He has mandatory federally protected training upcoming this year over this exact scenario (basically, not all of their training is federally protected, meaning an employer can’t retaliate over taking time off to do mandatory training). The military is obviously convinced it’s a real possibility.