So you're ruling one out? (Or even a large regional conflict, say, China vs Russia?)
(You're missing a couple things. Here you go: ----> ' e )
I am ruling them out, yes. None of the primary powers will find use in risking so much for so little. There are far too many non-state players with agendas that are easily manipulated by super-powers and when those manipulations go awry, you'll end up with country skirmishes, dictatorial replacements, government changes and ruling class upheavals. World wars have simply outlived their usefulness.
Additionally, NATO is fairly punkish but still wields the forum to create many alliances that, if caught early enough, will stop invasions of land, sea or airspace. One big guy at a bar ends up starting a fight with the entire bar? Not likely and even though he may land the first few punches, the rest of the bar will respond because in this particular case, the patrons are all off-duty cops.
China vs Russia would never be defined as a large regional war, lol but you did make a funny.