Complex sentence: It was then expanded upon in various "D&D" modules and sources, particularly a series of Gazetteers, many of which originally referred to the setting as "The" D&D "Game World".
Split into simpler sentences: It was then expanded upon in various "D&D" modules and sources, particularly a series of Gazetteers. Many of these publications originally referred to the setting as "The" D&D "Game World".