Fourth Shinobi World War

The beginning of the was declared by Madara Uchiha when the five Kage's and the leader of the Land of Iron unanimously refused to give him the Eight-Tailed Giant Ox and the Nine-Tailed Demon Fox for his Eye of the Moon 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 General 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.

Preparations for War
Both sides are gathering their strength and collecting information about the other side in preparation for the upcoming hostilities. Kisame gathered intelligence on Kumogakure's military strength and on Killer Bee while traveling with him everywhere hidden inside Samehada. The team of Anko Mitarashi tracks Kabuto Yakushi, which led them to Madara Uchiha's lair. Other Shinobi Alliance teams have fanned out to collect other information about Akatsuki and their hideouts.

Kabuto has formed an alliance with Madara, showcasing his use of the Summoning: Impure World Resurrection technique, increasing the forces of Akatsuki with the resurrection of dead members of the organization. The Five Kage have decided to hide the two remaining jinchūriki, Naruto and Killer Bee in a island in the Land of Lightning. Hiding Killer Bee and Naruto had the unintended result of allowing Naruto to learn to control the Nine-Tailed Demon Fox's chakra, much like the way Killer Bee has of the Eight-Tailed Giant Ox. Having been successful in his training, Naruto has exhibited increased speed and strength when utilizing the controlled chakra of the Nine Tails but lacks the same finesse that Killer Bee had exhibited in utilizing the Eight Tails', crashing into the wall and crushing rocks whenever he uses the Nine Tails chakra.

Despite being captured in the end and committing suicide to keep the information he held secret, Kisame was able to finish Akatsuki's preparations for the War by sending a summon shark with a scroll to his comrades divulging the proximate location of the Turtle Island. With the battle between the two forces seems to be on the horizon, Madara had dispatched Kabuto to retrieve the Nine-Tails and Eight-Tails with the revived Deidara but was stopped by Ōnoki, Akatsuchi and Kurotsuchi who was going to reinforce the forces on the Island Turtle. But Kabuto still made it out with Yamato, further adding to the intelligence sources that Akatsuki has on the Shinobi Alliance and also intending on strengthening the Zetsus with Yamato's powers.

Both the Allied Shinobi Forces and Akatsuki have amassed considerable forces for this war, 80,000 shinobi and samurai total make up the Alliance and 100,000 Zetsu clones and at least 24 warriors of note revived by Kabuto make up Madara's army.

Allied Shinobi Forces
The Allied Shinobi Forces created by the Five Great Nations and the Samurai of the Land of Iron consists of five main divisions, with Gaara of the Sand as the Commanding General. The 1st Division consists of midrange fighters and is led by Darui. The 2nd Division is made up of Close Range Fighters and is led by Kitsuchi. The 3rd Division is under the command of Hatake Kakashi, and features both close and midrange fighters. The 4th Division contains only long range fighters under the control of Gaara, who is also the commanding general of the entire army. Shikamaru is Gaara's right hand man and proxy general of the 4th division as well. Finally, the 5th division was created for the purpose of special operations, and features ninjas with unique skills. Mifune is the leader of these special operatives. There is also four special company formed for the war. The Medical Logistics Company led by Shizune comprises of medical ninja, the Ambush Company led by Kankurō, has the task to ambush the enemy forces. The third is the Sensor Company with Ao as captain, and finally the Intelligence Company headed by Inoichi Yamanaka is intended to gather information and relay it to Gaara for strategy's sake.

Akatsuki
Akatsuki, run by Madara Uchiha, has evolved since its first introduction. Its second in command is Kabuto Yakushi, and operate out of a base to the north. There are four living members: Madara, Kabuto, Sasuke Uchiha, and Zetsu. However, Zetsu has 100,000 clones ready for battle, which were somehow created using Hashirama Senju's power. Kabuto also has taken from Orochimaru the Summoning: Impure World Resurrection technique, and has used it to resurrect at least 21 known shinobi, who are as follows: At least one other kage was also present, as well as other unseen and unknown shinobi. Madara has even expressed the desire to use the seven tailed beasts in Akatsuki's possession to fight the war. They are now moving out, and it is presumed that they will continue to pursue the jinchūriki in Kumogakure.

Allied Shinobi Forces
Analyzing their own and their enemy's location, they have decided that Akatsuki will send a small fraction of their army by sea from the Mountain's Grave (Akatsuki's hideout) to Kumogakure, and that most of the army will travel by land. This would require the army to move through both Kirigakure and Yugakure. An immediate evacuation notice was sent to both cities, and they will most likely evacuate to the south, in the Land of Fire. The Ambush Company will be sent to that path in order to halt the enemy army, and the Medical Logistics Company will back them up. The Intel Squads are to be utilized to help inform the separate ambush groups of the nature of each enemy encountered, and the Sensor Company will be deployed to aid the ambushes. Each of the four fighting divisions are expected to remain on a steady path toward the enemy, but not straying far from the jinchūriki. The close-range divisions will venture further from Kumogakure, while the long-rangers will stay closer to home. It is unknown where the Special Operations division will operate.

Akatsuki
Much less is known about the Akatsuki strategy, except that their goal is still to secure the jinchūriki.

Battles
As both sides prepared for the war, Akatsuki continued it's standard methods of capturing the jinchūriki.

Capturing the Eight-Tails

 * Location: Sabu's Home
 * Combatants:
 * Akatsuki: Kisame Hoshigaki, Zetsu
 * Enka Ninja: Killer Bee, Sabu
 * Outcome: Kisame able to infiltrate the Allied Forces.

After tricking Taka into believing they had captured him, Killer Bee sought out the enka ninja Sabu to learn from him. Kisame Hoshigaki tracked him down with Samehada and the battle ensued. When the Fourth Raikage and his two C|bodyguards arrived, Kisame was thought to have been killed. This was however a unique clone created by Zetsu and the real Kisame was hidden inside Samehada, which Bee had claimed, to gather information on what the Allied Forces were going to do with the shinobi.

Battle on the Island Turtle

 * Location: Island Turtle
 * Combatants:
 * Akatsuki: Kisame Hoshigaki
 * Allied Shinobi Forces: Aoba Yamashiro, Killer Bee, Might Guy, Motoi, Naruto Uzumaki, Yamato
 * Outcome: Akatsuki finding the location of the jinchūriki.

By hiding in Samehada, Kisame was able to not only gather information on the Allied Forces base of operations but the location of the jinchūriki. Traveling with Bee to the Island Turtle he remained unnoticed by everyone until Naruto's new power allowed him to sense Kisame in the sword. As Kisame fled, he was encountered his old foe Might Guy and the two squared off in a final battle. Using his Daytime Tiger, Guy managed to capture Kisame but before he could reveal any information he killed himself with a shark summon.

With Kisame dead, the Allied Forces attempted to figure out what Kisame had managed to learn about them through the scroll he left behind. When the scroll opened, the trap activated, trapping everyone in a Water Prison Technique and another shark to take the information scroll back to Madara.

Battle for the Rinnegan

 * Location: Amegakure
 * Combatants:
 * Akatsuki: Madara Uchiha
 * Amegakure: Konan
 * Outcome: Madara obtains the Rinnegan, Amegakure loses its village head.

Madara Uchiha confronted Konan within Amegakure in order to obtain the Rinnegan from Nagato's corpse. Having prepared to fight Madara, Konan had integrated over 600 billion exploding tags into her paper jutsu, knowing that Madara can only stay intangible for five minutes and set off enough explosions to last ten minutes. With her chakra depleted, Madara revealed that he survived the explosions using the power of Izanagi with his right eye's Sharingan. After using a genjutsu to get Nagato's location from her, killing her in the process, Madara claimed Nagato's body and took the Rinnegan for his own.

Second Battle of Island Turtle

 * Location: Island Turtle
 * Combatants:
 * Akatsuki: Deidara, Kabuto Yakushi, Manda II
 * Allied Shinobi Forces: Akatsuchi, Aoba Yamashiro, Kurotsuchi, Motoi, Ōnoki, Yamato
 * Outcome: Yamato captured.

With the jinchūriki's location known, Kabuto volunteered to capture the jinchūriki. Kabuto chose the resurrected Deidara to accompany him and to set out to find the island by air. The Third Tsuchikage and his guards, being notified that the island turtle's location has been compromised, flew to the island to defend it from potential attack. The two parties intercepted each other en route and the Tsuchikage and Akatsuchi opted to fight Deidara while Kurotsuchi pursed Kabuto to the turtle.

The island turtle, which had moved from the previous location was quickly found by Manda II. The giant serpent flipped the entire turtle over stopping it's movement. Yamato, Motoi and Aoba left the inner part of the turtle shell and encountered Kabuto just as he and Kurostuchi arrived. Kabuto avoided their combined efforts by revealing that he had turned his body into a giant white snake, similar to Orochimaru. Figuring that the jinchūriki were too protected to be captured alone, he instead captured Yamato, the user of the First Hokage's Wood Release and returned to Mountain's Grave.

Trivia

 * Itachi Uchiha prevented an earlier potential outbreak of a Fourth Ninja War by carrying out the Uchiha clan massacre.
 * A Fourth Ninja War was also declared by Hiruko in the third Naruto Shippūden Movie, and would have pushed through if not for the efforts of select Konoha shinobi.