Which Pokémon games were the first main-series titles with worldwide online trading?

Pokémon Diamond and Pearl were the first main-series titles with worldwide online trading.

Released for the Nintendo DS in Japan in 2006 and internationally in 2007, the games used the Nintendo Wi-Fi Connection to let players trade Pokémon online. The Global Trade Station, or GTS, allowed players to request and exchange Pokémon with people around the world.

Earlier games supported local exchanges through link cables, infrared communication, or other nearby connections. Diamond and Pearl expanded that idea beyond the players physically gathered in one place.

The games also included local wireless features and online battles, so “online trading” should not be confused with the first Pokémon trade of any kind. The Nintendo Wi-Fi Connection service itself was discontinued in 2014, but the feature remains an important milestone in the series.