Which main-series Pokémon games introduced the Global Trade Station?

Pokémon Diamond and Pearl introduced the Global Trade Station, commonly called the GTS. The feature allowed players to offer Pokémon and request trades with players around the world through Nintendo Wi-Fi Connection.

The GTS was a major change from the local Game Link Cable trading used by earlier games. Players could deposit a Pokémon, specify what they wanted in return, and leave the request available for another player to complete, even when the two players were not online at the same time.

Diamond and Pearl were released for the Nintendo DS in Japan in 2006 and later worldwide. The games also supported online battles and voice chat, but the GTS is specifically the system associated with global Pokémon trading.