The Fourth Shinobi World War Arc in Naruto has very powerful villains and the Allied Shinobi Forces have struggled, even more so due to the use of Edo Tensei jutsu, a resurrection technique that causes dead shinobi to return to fight as “zombie” slaves for the user. Powerful shinobi, including former Hokages and even Naruto’s father, Minato, were revived. While the resurrection of these characters makes for interesting battles and confrontations, that’s not the main reason author Masashi Kishimoto introduced them.
During the war, Obito commanded tens of thousands of White Zetsu soldiers, but that number was not enough to confront the combined strength of all the shinobi in the world. He made a deal with Kabuto and accessed the power of the dead shinobi he summoned through the forbidden Edo Tensei jutsu: Akatsuki members, former Kage, Jinchuriki, and legendary warriors. This gives fans the chance to witness some legendary shinobi from the past who would otherwise never appear in the series, while also giving Naruto a chance to meet him. Enlightenment was necessary, even if only temporary, with his father. However, Kishimoto has another, more subtle reason for including so many “zombies” in his story, and it makes perfect sense within the context of the series.
Naruto needs opponents he can actually defeat without compromising his pacifism
Masashi Kishimoto revealed in a 2014 interview with Fuji TV that the main purpose of the widespread use of Edo Tensei Jutsu was to change the general way he was using it. He stated that after the Pain Arc, Naruto never actually intended to kill his opponents, instead preferring to reason with them and attempt dialogue. This fits Naruto’s development as a character after Pain asks him to come up with his own answers to the violence of the shinobi world. Kishimoto said that this was also the spirit of Shounen manga (at that time) and he also had to follow this path. However, in his opinion, this quickly killed the mood of the story, so he came up with the brilliant idea of reintroducing the revived ninjas.
Basically, the followers of Edo Tensei (and Zetsu clones) are there so the good guys can beat someone up and kill them without feeling too bad about it. As such, Kishimoto was consistent with the style of previous Shounen manga but also sought to put his own unique spin on it. Of course, on top of that, fans will also get to see old favorites like Zabuza, Minato Namikaze or the First and Second Hokage, along with a host of other great warriors from the past whose names are well known. they have been mentioned throughout the series. Finally, Edo Tensei is also a way to introduce Madara into the story and fully revive him in the finale. The war was sparked by the threat of Madara leading the army so it was important to find a way to revive him.
However, while the need for fanservice and plot is also responsible for the widespread use of Edo Tensei, what is most important is that Kishimoto came up with this innovative solution to ensure that, while NarutoAs he moves away from his continued path of violence, his story will not lose the action-packed rhythm that has made it so popular with fans.
Source: Kobayashi Interview with Kishimoto: Extended Summary