Each one has their own independent storyline and system mechanics.
The standard game comes with an independent campaign for the Imperium, Necrons and Tyranids, and a paid expansion adds one for Chaos as well. MULTIPLE CAMPAIGNS: You are no longer restricted to playing through an in-depth campaign as only the Imperial Navy.PvP is for the most part the same as before, with set modes for ranked PvP and more flexible modes for skirmishes against NPC opponents. If you're just starting BGA2 and are a veteran of the first game, you would do well to read through and understand the following extensive list of updates that have been made to the gameplay which are mostly relevant to the Campaigns.
If you're looking for the Wiki for the original, see Battlefleet Gothic: Armada Wiki.
Quite a number of changes have been made to the gameplay. The sequel to Battlefleet Gothic: Armada, this game takes place over 800 years after the first game, at the turn of the Millennium 41.