Fourth Great War
This is the only war in which shinobi forces did not fight against each other, but together as one against Akatsuki. It appeared that the man behind the mask was Madara Uchiha, who later was revealed to be Obito Uchiha. He wanted to carry out Madara’s plan of Infinite Tsukoyomi to bring false peace. But at end it is revealed it was Black Zetsu’s plan all along to revive its creator Kaguya Ōtsutsuki.
First, the war broke out to protect Naruto and Killer B, the only remaining Jinchuuriki that were needed by Akatsuki to revive the Ten Tails. Kabuto who also joined hands with Obito revived almost all the Legendary Shinobi with the help of Reanimation Jutsu. And Obito had also created thousands of White Zetsu as well. On the other side, all the Five Great Nations, and Samurai of the land of Iron came together for the first time in history to stop and protect the Eight and Nine tails Jinchuuriki from falling into the hands of Akatsuki.