Imagine the entire Akatsuki invading the 5 ninja villages one by one. Each village they would encounter would be utterly annihilated. Sure the villages that haven't been attacked yet would learn of this and could join forces, if they would even agree to it. I think the Akatsuki would get to atleast 2 villages before that happened. At this time there wouldn't be enough Kage level ninjas to counter them. It would be the three remaining Kages, Jiraiya, Danzo, and Killer Bee. Plus Obito could have sent all the Zetsus to one village, which would probably wipe out that village aswell, or atleast severely cripple it.