Fourth Shinobi World War

The beginning of the 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. The daimyo of the Five Great Shinobi Countries and the Fifth Hokage later join the alliance as well.

Trivia

 * Itachi Uchiha 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 in the third Naruto Shippūden Movie, but that declaration never came through.