Complex sentence: DCS modules that can plug into DCS World include aircraft, maps, ground units, campaigns, etc. Not only does DCS World include modules developed internally by Eagle Dynamics, but it also includes those by certified third party developers.
Split into simpler sentences: DCS modules that can plug into DCS World include aircraft, maps and ground units. Modules for DCS World include modules developed internally by Eagle Dynamics, as well as those by certified third party developers.