|Please note that this is the Narutopedia's article on the episode. If you are looking for the article on the manga chapter then you should head to Declaration of War.
Declaration of War (宣戦布告, Sensenfukoku), is episode 205 of the Naruto: Shippūden anime.
Naruto thinks of Tobi's words about Sasuke. Tobi arrives at the summit room and teleports Sasuke, then Karin to a safer location. Tobi then reveals the origin of the tailed beasts, as the Ten-Tails. He reveals that his plan is to revive the Ten-Tails and become its jinchūriki, and then cast an infinite Tsukuyomi on the moon giving him control over everyone on the planet. Tobi asks the Kage to hand over the remaining tailed beasts. When they refuse, Tobi declares the Fourth Shinobi World War and leaves. The Kage agree to the formation of the Allied Shinobi Forces, Mifune also consents to join. Sakura arrives at Naruto's location, and says she has something to tell him.