What happened to humanity before the events of Pokémon Pokopia?

Before the events of Pokémon Pokopia, humans left Earth for outer space.

The game’s logs reveal that unexplained phenomena gradually made the landscape inhospitable to life. Humanity eventually departed the planet, leaving Pokémon behind in a world whose habitats had deteriorated.

The humans could not take all their Pokémon with them, so they stored Pokémon in a massive computer system designed to continue operating after the departure. The system could release selected Pokémon if it began to fail, creating part of the mystery that Ditto and Professor Tangrowth investigate.

This backstory explains why Pokopia begins with abandoned structures and damaged habitats rather than an ordinary Pokémon society. It also distinguishes the game from stories in which humans simply disappear without explanation. The outer-space departure is part of the game’s larger environmental and science-fiction premise.