War will have more than one part imo.
Firstly will be against the Marines defending Marejois. These include Akainu, Admirals, Vice Admirals, SSG (if not defeated prior), etc. Allies involved are mainly the Strawhat Fleet and Supernova, with Whitebeard Remants, former Roger Pirates and other allies potentially being involved. This will play outmore like Marineford/Paramount War with the SSG replacing the Shichibukai and upgraded Pacifista.
Part 2 is the WG in its entirety. These are Im, Gorosei, Kong, CP-0, whomever else. Allies mainly involved are the Revolutionaries and allied Kingdoms (Alabasta, Dressrosa, Prudence, etc) and whoever didn't fall during Part 1. It will take some time to reach Mariejois so there will be a reset here that allows for recovery.
Part 3 is, imo, Blackbeard and Shanks at God Valley. I fundamentally believe the Rocks storyline is being set up now to culminate into something with these 2 on this specific Island that the WG hid away. Black and Red, Chaos and Order, both the living will and actual son of Rocks, BOTH antagonists to Luffy and fundamentally the final goals in this series..
Part of my theory on how I believe this series will conclude. We'll see what happens