Eye of the Moon Plan

The is Madara Uchiha's ultimate plan that was later adopted by Tobi as well which the Allied Shinobi Forces intend to stop during the events of the Fourth Shinobi World War.

The Plan
While outwardly the Akatsuki believed they were collecting the nine tailed beasts to be used to become a dominating power in the world as a means to peace, Tobi used the organisation to gather the tailed beasts with the intention of combining them back into their original form: the Ten-Tails. Then, he would become its jinchūriki and with the god-like powers he would be granted by this, Tobi would project his Mangekyō Sharingan on to the moon, the prison of the Ten-Tails' body, to cover the world in an. The end result of the plan being that he would control every living being, ending all conflict by purging free will itself. However, during the attack on Konoha, Tobi's statement of "starting a war to bring peace" is part of his ideal that the end result justifies the means. Tobi has also noted that he wants to create a world where heroes do not have to make pitiful excuses over graves and put an end to all the ills in the world, by removing the agency of all living creatures.

Progress of the Plan
Though Tobi obtained seven of the nine tailed beasts, only the final two tailed beasts: the Eight and Nine-Tails, remained out of his grasp. After Taka and Pain failed to capture the two tailed beasts respectively, through Sasuke managed to bring him a part of the Eight-Tails' tentacle, Tobi decides to discard all caution and reveal himself, using Madara's name to commence the plan. Prior to revealing himself to the Kage at the Kage Summit in the Land of Iron, Tobi has White Zetsu lure them to Sasuke Uchiha and his team in hopes the ninja leaders would be weakened enough to be easily taken hostage to negotiate their freedom in exchange for the last two living jinchūriki, Killer B and Naruto Uzumaki. This, however, ended in failure, due to Danzō Shimura escaping during the chaos while combined forces of the Kage, their bodyguards, and Mifune overwhelmed Sasuke. Sending Sasuke into the other dimension with Karin, Tobi introduces himself as Madara while revealing this plan to the four Kage. However, they refuse to hand over Killer B and Naruto while forming the Allied Shinobi Forces to prevent Tobi from going through with his Eye of the Moon Plan.

At the end of the first day of the Fourth Shinobi World War, Tobi took the Kohaku no Jōhei and Benihisago that each contained one of the Gold and Silver Brothers, and having already collected a portion of the Eight-Tails from the tentacle Sasuke captured, Tobi intends to put the plan into motion by the end of the following day. Later, while fighting Naruto, he had the Demonic Statue of the Outer Path swallow the Kohaku no Jōhei and Benihisago in order to revive an incomplete Ten-Tails, claiming that the monster would still have enough power to be sufficient in completing his plan.

Upon the real Madara's arrival at the battlefield, he witnessed the Ten-Tails' revival being incomplete, along with his revival being different from what they originally planned, he believed Tobi had been impatient, and decided to capture the Eight and Nine-Tails to complete the plan, noting that there was still time.

Trivia

 * Tobi has blamed Naruto for the plan's slow progress, due to his constant interference.
 * Tobi noted that he would eventually sync Sasuke Uchiha with the statue. However, currently whether his intent is to simply add another person to the depleted Akatsuki extraction team, or something grander, is currently unknown.
 * Part of the plan was for Nagato to resurrect Madara with the Outer Path: Samsara of Heavenly Life Technique. Madara was instead brought back to life via the Summoning: Impure World Reincarnation by Kabuto Yakushi.