What was the first Pokémon version released internationally as a paired set?

Pokémon Red and Blue were the first Pokémon versions released internationally as a paired set.

Japan originally received Pocket Monsters Red and Green. For overseas markets, Nintendo used the revised Japanese Blue version as the technical and graphical basis for the games, while presenting the pair as Pokémon Red and Pokémon Blue.

The two versions share the same main adventure but contain version-exclusive Pokémon. That design encourages trading through the Game Link Cable, since completing the original Pokédex normally requires access to both versions or exchanges with another player.

North America received Red and Blue on September 28, 1998, and the pair later reached Europe in 1999. The naming difference is an important historical detail: Japanese players began with Red and Green, while international players generally began with Red and Blue.