The Guardian God War was being held on a barren island in the Island Secret Realm.
The island had been transformed by the Pokémon League and the Tapu Family into one suitable for battle. Pokémon that fought in water, air, or on land could all find suitable venues there.
The reason the Guardian God War was not being held on Alliance Island like the World Championship was because the aftermath of god-level battles was simply too uncontrollable.
A Pokémon on Giant Dragonite's level could destroy the Pokémon League's venue defenses with a single Hyper Beam.
Therefore, the Pokémon League had established a cooperative relationship with the four Island Kings and the Tapu Family, setting the God War's location in the Island Secret Realm. With the Tapu Family modifying the venue and setting up defensive facilities, the God War could proceed without a hitch.
After all, the four island gods were all Legendary Pokémon. Supervising a Guardian God War was no problem for them.
Furthermore, the island was close to the sea, so Water-type Pokémon would not be unable to unleash their full strength from fighting inside Alliance Island.
November 9th, the day before the God War.
The participating members from every country had basically all arrived on God War Island.
In fact, not many countries were participating in this God War. There were fewer than twenty in total, and quite a few countries had sensibly forfeited outright.
After all, not every country possessed Guardian God Level battle strength. The ceiling for many small countries was Top Level battle strength. There were only sixteen Legendary Resources in total, likely not even enough for the major countries to divide among themselves...
China, Japan, the United States, the United Kingdom, France, Russia, Germany, India... Every one of these countries could field several Guardian