Third Shinobi World War

The was the third of the four shinobi wars that involved the majority of the shinobi villages. It took place more than ten years prior to the beginning of the series. Because of a decline in national power, the reign of the Five Great Shinobi Countries was crumbling. Along their borders, skirmishes with smaller nations broke out all the time. The prolonged conflicts gradually spread their flames far and wide, until at last it developed into an all-out war. The conflict turned into an unprecedented war of attrition, tormenting all nations with a shortage of war potential. Not even excluding a great power like Konoha, very young children, some of whom were barely out of the Academy were thrown onto the battlefield, eventually losing their young lives during the war.

War
Konohagakure and Iwagakure fought across Kusagakure after the latter had infiltrated it in order to lay siege to the border of the Land of Fire. It was not until the destruction of the Kannabi Bridge that the war began turning in Konoha's favour. Iwagakure was also known to have been fighting Kumogakure with various skirmishes between the two villages. Sunagakure also participated in the war. Kumogakure was also seemingly a part of this war, with at least Konohagakure clashing with shinobi from this village, specifically Minato and A. This is also the war in which the Third Raikage died and the Fourth Raikage was appointed. Kirigakure also partook in the war against Konohagakure and made Rin Nohara into the jinchūriki of the Three-Tails. Rin chose to die by Kakashi's hands, rather than be used as a tool to destroy her own village. The Kiri shinobi were adamant in retrieving Rin's body and not allowing it to fall into enemy hands. Rin achieved this by letting herself be stabbed by Kakashi's Chidori which not only stopped the Three-Tails from being released but also resulted in Rin's death. Grief-stricken Obito Uchiha, who unbeknownst to his teammates, had survived and was a witness to Rin's murder, massacred the Kiri shinobi by himself, despite their best attempts. Some time after this, Madara Uchiha would pass away, but not before passing his plans onto Obito to fulfil until the time of his resurrection. Ao from Kirigakure also defeated a member of the Hyūga clan and took the member's Byakugan for his own right eye socket. The Battle of Kikyō Pass took place in this war.

The war that swallowed up shinobi from every land came to an end after an armistice agreement between Konoha and Iwagakure, which were the principal aggressors of the war, was concluded. In the anime, the Tsuchikage was more reluctant to accept the peace treaty, only accepting it after Minato single-handedly stopped an invasion consisting of a thousand Iwa shinobi.

Effects
In Konoha, although the war had been proceeding favourably for the village, the Third Hokage established a policy of reconciliation to bring an end to the fighting with an unprecedented offer to not seek reparations from Iwa. Advocates for the war opposed Hiruzen's seemingly weak decision, and to keep dissatisfaction in the village in check, he decided to step down as Hokage. The Konoha shinobi that received the most attention for their war efforts in the village were the Sannin and the surviving members of Team Minato. Out of the two teams, Minato who was the key factor in the war that gained the moniker of alongside Orochimaru, were the only two candidates village officials put forward to succeed Hiruzen. Ultimately, it was Minato who became the Fourth Hokage.

Between Fugaku Uchiha not receiving praise for his work during the war alongside his name not being put forth to become Hokage, members of the Uchiha clan came to despise village officials. Itachi Uchiha was traumatised by the violence of the war and grew to seek peace at any cost because of it: an experience that would lead to the Uchiha Clan Downfall and prevent his clan triggering the Fourth Shinobi World War. However, Obito Uchiha who had been saved from death by Madara Uchiha during the war eventually caused the next world war, after witnessing Rin Nohara die and taking on his saviours identity.

In Sunagakure, Sasori earned fame as, due to his ingenious puppets dyeing the sand red with his enemies' blood. In Kirigakure, Ao gained a Byakugan from a Hyūga clan member he killed during the war, which in term lead him to be known as. In Konoha, Kakashi Hatake eventually gained fame throughout the shinobi world as, after he gained a Sharingan from a dying Obito during their mission to destroy the Kannabi Bridge.

In Iwagakure, the Jinchūriki of the Five-Tails, Han became known worldwide for his prowess with steam ninjutsu.

In Amegakure, Yahiko, Nagato, Konan, and many other shinobi formed a group that eventually fought the rule of Hanzō. Initially, they were merely preaching peace for Amegakure. They were supported and even invited to negotiate peace by Hanzō himself. In the anime, they unknowingly disrupted Danzō's attempt to disrupt a ceasefire between Konohagakure and Iwagakure with a group of Root members disguised as Iwa shinobi attacking Yahiko, Konan and Nagato, resulting in Nagato unwillingly summoning the Demonic Statue of the Outer Path which killed a few of the Root men before Yahiko brought Nagato back to his senses. Once Nagato had passed out, Yahiko and Konan retreated, bringing Nagato back to their hideout to recover. Danzō immediately arrived at the location and to ensure peace didn't exist between Iwagakure and Konoha, had his surviving men collect the dead bodies and erase Root's trace in the incident before he and his men met Hanzō, Danzō revealing the corpses of his men were actually those belonging to Hanzō's clan which saw the Akatsuki being framed and portrayed as murderers or wolves in sheep's clothing who if unstopped would eventually take over the country. Hanzō later sided with Danzō, the two men working together to banish the threat of Akatsuki who Hanzō feared had become power hungry with the intention of unsurping his power. Danzo later approached Akatsuki, disguised as "Kanzō" and informed the group Hanzō wished to meet them, resulting in the group celebrating. As that happened, Konan who was on patrol was captured. When Yahiko and Nagato arrived at the location, they discovered the meeting was a trap with Danzō and his Root Anbu in attendance while Hanzō held Konan as a prisoner, demanding Nagato kill Yahiko in exchange for Konan's life or they would all die if Nagato refused. Not wanting Nagato to live with the guilt of killing him, Yahiko intentionally committed suicide by impaling himself on the kunai Nagato was holding before he slumped to the floor, dead. This left Konan devastated and prompted Nagato to first stop the kunai from hitting himself and Yahiko's dead body. He then rescued Konan but at the cost of having his legs badly damaged by Hanzō's Fire Release: Exploding Flame Formation. When Root and Amegakure shinobi approached them, intending to eliminate them, Nagato summoned the Demonic Statue of the Outer Path and by using the black receivers which embedded itself into his back, it was able to slaughter all of the Amegakure and Root shinobi who had been instructed to kill Nagato. Not completely satisfied, Nagato also attempted to kill Hanzō who fled via the Body Flicker Technique. With Yahiko and the other remaining members of the group dead, Nagato and Konan were the only survivors left. Nagato was later confined to a machine for the rest of his life, his body having become severely emaciated as a result of him linking with the statue. He later became the new leader of Akatsuki while slashing his forehead protector, revealing he no longer wanted to be associated with Hanzō. Eventually, a civil war erupted, splitting Amegakure with the battle ending when Nagato's Six Paths of Pain eliminated the members of Hanzō's fraction while Nagato, using Yahiko's body confronted and later killed Hanzō.

Trivia

 * It was claimed in Naruto Shippūden the Movie: The Will of Fire that during this war, the missing-nin Hiruko was actively working to finish his Chimera Technique and had tracked Kakashi in order to brand him with his Puppet Curse. He claimed that, eventually, the Third Hokage ordered his assassination to be carried out by his former friends, the Sannin.
 * It was claimed in Naruto Shippūden the Movie: The Lost Tower that Rōran was destroyed during this war.
 * In Six-Tails Unleashed, the Third Hokage made a peace treaty with the Tsuchigumo clan sometime during the war.
 * In the anime, Danzō was shown to be a driving force in this war, having members of Root transform into Iwa-nin and frame the village to cause war between the two villages.