Why weren't the four Hokages reincarnated by Kabuto in the Shinobi war? In the anime, Kabuto reincarnated Asuma, Dan, Hizashi etc from Konoha to battle against the allied Shinobi forces. Earlier, Orochimaru reincarnated the 1st and 2nd Hokage to battle against the 3rd. Why didn't Kabuto reincarnate the four of them to fight against the alliance? Couldn't they be reincarnated again or wasn't that part of Tobi's plan?
Actually, Kabuto can't revive the 1st and the 2nd Hokage simply because Hiruzen Sarutobi (3rd) sealed them away using the Dead Demon Consuming Seal. 

While the reason Orochimaru can revive the two is because he ripped the belly of the Demon (Shiki Fuujin) who consumed their souls in Naruto chapter 618, page 4.