Fourth Great Shinobi World War

From Narutopedia

The beginning of the Fourth Great Shinobi World War (第四次忍界大戦, Daiyonji Ninkai Taisen) was declared by Madara Uchiha when the five Kage refused to give him the Eight-Tailed Giant Ox and the Nine-Tailed Demon Fox for his Moon's Eye Plan. Madara has stated that he will use the seven tailed beasts already captured by the Akatsuki in combating the ninja world. The Fifth Kazekage, the Fifth Mizukage, the Fourth Raikage, the Third Tsuchikage, and Mifune have agreed to form a Shinobi Alliance, pooling their resources against Madara. They intend to invite all of the Five Great Shinobi Countries including Konohagakure into the alliance, but they do not trust the Sixth Hokage. Instead, they went for Kakashi Hatake, a trustworthy and powerful shinobi, to represent the village.

Years earlier, Itachi Uchiha had prevented the outbreak of a Fourth Ninja War by carrying out the Uchiha Clan Massacre. The Fourth Ninja War was also declared again by Hiruko during the third Naruto Shippūden Movie, but that declaration never came through.