The Kage Summit.
The Five Kage Summit (五影会談, Gokage Kaidan) was a meeting between the five Kage of the ninja world to discuss recent developments concerning Akatsuki and the tailed beasts.
Background
Since its formation, Akatsuki had been working on capturing the nine tailed beasts or their jinchūriki. At the start of Part II, Akatsuki had captured two tailed beasts; the Five-Tails and the Seven-Tails in the anime. As Part II progressed the organisation also obtained the One-Tailed Shukaku, the Two-Tails, the Three-Tails, the Four-Tails, and the Six-Tails in the anime. The capture of seven tailed beasts had come with great losses for Akatsuki, so the organisation's founder, Tobi, dedicated extra resources to the remaining beasts' capture.
To capture the Eight-Tails, Tobi sent former Konoha ninja, Sasuke Uchiha, and his team to the Land of Lightning to apprehend Killer B. Much of the Valley of Clouds and Lightning was destroyed during the battle, and at its conclusion Killer B appeared to be captured. Killer B's brother, the Fourth Raikage, was enraged by the news and demanded a meeting of the Kage to finally do something about Akatsuki and possibly save B. In reality, B only pretended to be captured, and Akatsuki continued searching for him.
As summons for the summit were sent out, Konoha was attacked by the recognized Akatsuki leader, Pain. Tobi had sent Pain to find Naruto Uzumaki, the jinchuriki of the Nine-Tailed Demon Fox. Naruto was able to elude capture and defeat Pain, but most of the village was destroyed. Additionally, the Fifth Hokage was left in a coma, necessitating she be replaced by Danzō, the candidate for the position of Sixth Hokage.
Meeting
The building where the summit took place.
For the meeting, the Kage were allowed to bring two bodyguards. The Kage and their bodyguards departed for the Land of Iron, a neutral, samurai-controlled country. Mifune, the general of the Land of Iron, presided over the summit. When all were present, the Fifth Kazekage began the discussion. As the former host of the One-Tailed Shukaku, he had long considered Akatsuki a serious threat and requested cooperation between the villages, something only the Fifth Hokage had agreed to. The Third Tsuchikage, scoffed at the idea of the villages working together, citing the need for the villages to look after themselves. Nevertheless, he expressed concern for how many tailed beasts Akatsuki had obtained.
The Raikage, frustrated with the discussion thus far, crushed the table in front of him. The bodyguards came to their Kage's aid but order was quickly restored. The Raikage voiced his distrust of the other villages, all having previously employed Akatsuki and all having had an Akatsuki representative at some point in time. Only his own Kumogakure had never had the same vices. The Tsuchikage defended Iwagakure's actions, saying that he was forced to employ Akatsuki because of Kumogakure's relentless efforts to amass power and techniques. Danzō made no comment, and the Kazekage, having been unaware of Sunagakure's use of Akatsuki, was disgusted. The Fifth Mizukage, when confronted with allegations that Akatsuki had been created in Kirigakure, offered only her desire to find out how Akatsuki worked in to her village's history.
To get the meeting back on track, Danzō revealed Madara Uchiha's involvement with Akatsuki. Because of this revelation, Mifune proposed having the ninja villages join forces against Akatsuki, to be led by one of the Kage. For this position he nominated Danzō, believing Konoha's demon fox to be the only tailed beast not yet captured by Akatsuki. When questioned by the remaining Kage, Mifune pointed out why they were unfit for the job: the Kazekage was too young; the Tsuchikage was too old and had used too much of Akatsuki in the past; Kirigakure had suspicious connections with Akatsuki; and the Raikage's destruction of the table showed him to be too easily overcome by his emotions.
Before the Kage could come to an agreement, Ao, one of the Mizukage's bodyguards, revealed that Danzō was manipulating Mifune's actions with a special technique. Before he could be pressed on this matter, Zetsu of Akatsuki appeared and told the Kage that Sasuke Uchiha was nearby. The Raikage apparently killed Zetsu and left with his bodyguards to fight Sasuke, and the Kazekage followed with his own bodyguards soon afterwards. While the Raikage was gone Danzō explained that his manipulation of Mifune was because what he perceived to be a need for the ninja world to be brought together in order to stop the endless conflicts. When Sasuke arrived at their location Danzō fled with his bodyguards, he being Sasuke's target.
Sasuke was unable to follow Danzō, being stopped by the Mizukage and Tsuchikage. Before he could be killed by the latter he was saved by Tobi, who sent him away to recuperate. When the Raikage and Kazekage returned, Tobi told those in attendance about his Eye of the Moon Plan: his desire to unite the tailed beasts back into the original Ten-Tails so that he might bring the whole world under his control. To that end he requests the Kage give him the Eight-Tails and the Nine-Tails. When the Kage refuse, Tobi declares the start of the Fourth Shinobi World War and leaves.
Resolutions
With these new developments, the Kage and Mifune agreed to form a Shinobi Alliance, pooling their resources to battle Akatsuki and their seven tailed beasts. With the revelation that Kumogakure still had Killer B, and the Hokage's previous actions, A was selected as the group's leader. They choose not to work with Danzō but, knowing Konoha's contributions would be vital to the war effort, agree to inform Konoha of their plan through other channels: Kakashi Hatake.
In terms of tactics, the Kage decide to immediately secure B and Naruto to make sure they do not fall into Akatsuki's hands. The Tsuchikage suggests using the two on the battlefield to bring the war to a swift end, but the other Kage disagree, believing that would make it too easy for Akatsuki to capture them. Instead, protecting them both will become a top priority. The Kage Summit ends, and the Kage depart to inform their respective villages and daimyō of their decisions.