If you are looking for the exact moment the "War Arc" kicks off in the anime, it begins with the mobilization of the five divisions.
Are you planning to the war arc, or would you like a filler-free guide to get through the battles faster? when does the 4th ninja war start
Immediately following the Five Kage Summit in the Land of Iron. Tobi appears before the Kage and announces his plan to collect the Eight-Tails (Killer B) and the Nine-Tails (Naruto Uzumaki) to complete the Eye of the Moon Plan. When the Five Kage refuse to hand over the Jinchuriki, Tobi officially declares the Fourth Great Ninja War. If you are looking for the exact moment
While the declaration happens at the Summit, the begin shortly after the Allied Forces mobilize. Tobi appears before the Kage and announces his
The political start of the war occurs well before the fighting, when (disguised as Madara) declares war on the Five Great Shinobi Nations during the Five Kage Summit. Anime: Episode 205, "Declaration of War" Manga: Chapter 467, "Declaration of War" 2. The Official In-Universe Date
The Fourth Shinobi World War officially begins in of Naruto Shippuden , titled "For My Friend," and Chapter 515 of the manga.