Which Pokémon game first introduced the Global Trade Station?

Pokémon Diamond and Pearl first introduced the Global Trade Station.

The Global Trade Station, commonly called the GTS, used the Nintendo Wi-Fi Connection to let players offer Pokémon and request specific species online. Players could leave an offer for others to find and complete, allowing trades even when the two participants were not online at the same time.

Diamond and Pearl were released for Nintendo DS in Japan in 2006 and introduced the Sinnoh region. Their online features also supported internet battles, voice chat, and broader communication between players.

The GTS was not the same as the traditional Link Cable trade system. Earlier Pokémon games supported local trading, but Diamond and Pearl made worldwide asynchronous trading a central feature. The Nintendo Wi-Fi Connection service was later discontinued, although the idea of a global online exchange continued in later Pokémon games.