Voxica Island

Voxica Island, often just referred to as Voxica, was the original home of the Voxican (human) race. It was destroyed by Heiress to power the Realm Tree of the island, which was then transplanted onto Fort Voxica to save the human race.

The island was a beautiful (if small) landmass sitting in the Quiet Sea. Its primary settlements were the central city of Jailtown, Havenhill, the primary farming community, and the three bases of the original clans: Redshield (of the Everguards), Dawn's Acre (of the Lightwardens), and Prospera (of the Goldbloods).

The World Beyond the Island
The world they left behind is not the same one from Pokémon canon; there is no Kanto, Hoenn, Unova, or the like. Voxica Island was a mysterious piece of land that characters were unable to leave-- whoever washed up or set out for there in the twenty-odd years since its rediscovery had been trapped on it. Humans could have been from other lands or regions within the world before arriving on the island, but nothing from Pokémon canon.

All regions beyond the island were destroyed with the rest of the realm. Only humans from the island itself were saved (though even then, a good number of those perished, too).

Last Mentions in Lore
"The damage that the Queen had dealt to the island was irreparable, and the blight to its source of life and magic (the Realm Tree) too great. The freed creators explained that the human world was on its last lap around the local star, and would fade into nothingness when the power of the Tree ran dry.

The solution was to leave.

With the shattered remnants of their beloved island and fading world left behind them, all of the humans who managed to escape are now onboard Fort Voxica-- a massive stone fortress-ship headed into Ultra Space. Their home is dead and gone, and the future has many mysteries in store."