What keeps you bound on this earth, I am asking that because that is the only way you can understand what the subordinate of Orichimaru did? Let’s back a bit and start this story focusing on Kabuto (sub-ordinate of Orichimaru). If you don’t have any slightest idea what happened with Orichimaru? Then let me help you. Sasuke Uchiha killed Orichimaru or better to say he absorbed him. When Orichimaru was trying to absorb Sasuke and it turns out a bit back fired and Sasuke absorbed him instead. But when Sasuke was fighting with his brother Itachi Uchiha he released the chakra he was suppressing to control Orichimaru and on the final stage when Sasuke has no longer control over Orichimaru chakra. He Emerged and attacked on Itachi but no one can stand a master like Itachi and he finished Orichimaru with a single blow. Now back to Kabuto when he realized that Orichimaru was dead he experimented. He fussed his cell with Orichimaru cell gaining power of Orichimaru though he wasn’t as powerful as him and the cells of Orichimaru started spreading in his body slowly-slowly. He even masters the technique to bring dead into living and thus making his own army of dead to fight in the living world with the Kages and the ninja alliance. He resurrected all the formal strong shinobi he can and even resurrected the blood line limit users. Though he was unable to resurrect first and second Hokage as their soul were sealed by the third Hokage during the battle between Orichimaru, when he used the dead world resurrecting technique. The technique was quite simple, it needs a living sacrifice to bring back the dead as the living sacrifice acts as a vessel for the dead to reside. The technique is quite dangerous as the one who is dead is being controlled by the person who resurrected them. They can’t defy the order of the person, even though they don’t want to do. The person who is dead can use all the technique he was using when he was alive, making them more dangerous. The body of the dead is not fragile and can’t be destroyed; Even if it’s burst in pieces, the body will regenerate itself. Dead can’t be killed again and the only way to stop them is to seal their souls as the third Hokage did. But the person who will seal the souls will die eventually. Really a troublesome technique, but the technique has flaws. The only way to undo the technique is to put the user on his/her knees and make him say “Release” (this is what Kabuto told the sharigan user Madara Uchiha). Well I am not going to buy his stuff as his plan from starting is to betray Madara. This is what I believe, to undo the technique you have to let the soul of the dead free. There is always something that binds us to the living world even though when we are dead. So what we need to do is to unbind the dead from the links of the living world then only the spell will break. There must be another and quick way too, But let’s assume that it is unknown to us and the only option to fight with the dead is to crush the link or unbind them from the living world.
The fight is already started, the dead walking into living and killing them. At this point it’s really impossible to say what turn of event this fight will take.