>>30420522This probably depends on the context of the war.
If it's a POKEMON War, Sinnoh wins without contest. No other region contains literal gods, and it only takes the cooperation of 3 Pokemon to enlist them into said war.
If this is a human war, with trainers enlisted as soldiers, things get a little fuzzier. Canonically, Unova overall has the strongest Pokemon obtainable by man, as its got both a long list of canonically strong but capturable/recruitable legendaries like the Musketeers and Tao Trio, in addition to their list of regional Pokemon being naturally high in power level (read: high BST). Assuming we dive all the way in, the Unova region could realistically enlist Kyurem-B/W into their army, which is a tideturning force in itself. Unova would be the most likely to win any war, with a single exception.
I don't believe Kalos could lose any defensive war. While the region is pretty sparse otherwise, the legendary trio there is not only canonically recruitable, but Zygarde additionally is a continental defender. While they couldn't take an aggressive war very well, Zygarde (without human intervention) would go 100% to defend Kalos against intruders. Even with Kyurem, Unova isn't going to win an offensive war against the giver of life, the creator of death, and a Pokemon only passed by Arceus and Mega Fug in raw power. Alola has this to a similar degree, but due to the random natures of its legendaries (UBs) it's only really got it's own regional Zygarde to help defense. It could realistically lose to a Unovan offensive front.
Other regions I'd argue are up to debate, but they're not going to be able to beat Unova, and wouldn't be able to push a foward position against Kalos or Alola. If the Sinnoh region could somehow get Dialga, Palkia, or Giratina on their side they'd shoot up the list, but considering how we've seen that go when Team Galactic tried to do it, I doubt humans would be capable of accomplishing the feat.
