Somehow. It has to. [It always does. It's a bitter thought, but not any less accurate. Technically the war itself is centered around Killer Bee and Naruto, but that's another can of worms.]

Akatsuki's leader, Uchiha Madara, used Sasuke's infiltration of the Kage Summit to declare the war, for starters. Reports state that Sasuke was nearly killed, but Madara intervened on his behalf.

It's peculiar, considering the other four he came in with were abandoned. And there's few members left of the organization besides them now that most have been eliminated. That he went to such lengths for Sasuke guarantees he's crucial to Madara's plan.