Konoha Crush

The was the planned invasion of Konohagakure by Orochimaru and Sunagakure during the Chūnin Exams. Though Orochimaru was the mastermind of the invasion, the Fourth Raikage insinuated that the invasion was a secret plot of Danzō Shimura with Akatsuki to dispose of both the Third Hokage Hiruzen Sarutobi and the Fourth Kazekage.

Background
For years, Sunagakure suffered a series of budget cuts by the daimyō of the Land of Wind, weakening the village and thus re-routing ninja missions to Konoha. One day, Orochimaru, a missing-nin from Konoha who founded Otogakure, approached the Fourth Kazekage with the proposition of a joint invasion using the Chūnin Exams hosted in Konoha as a cover to attack. Orochimaru, at some point, murdered the Kazekage and assumed his identity on the day of the Chūnin Exams' final matches to make controlling Sunagakure easier. Orochimaru also planned for Kimimaro to take part in the invasion but was stricken with illness before the invasion. Kabuto mentioned had this not happened, the invasion of Konoha would have been a lot worse for the village.

The attack was meant to be fought on two fronts: Sunagakure's jinchūriki Gaara would make it to the final rounds of the chūnin exams and release his tailed beast Shukaku from the centre of the village. While Konoha was preoccupied with the One-Tail, Sunagakure and Otogakure forces would break through the walls surrounding the village. Orochimaru, having only one goal for the invasion, would fight and kill his old mentor and the current Hokage, Hiruzen Sarutobi. Though Konoha never knew the exact details of the invasion or who would be invading, it suspected an attack and had its forces prepare for the worst.

Invasion
When Gaara was injured by Sasuke Uchiha during the finals, he was left mentally unsuited for fulfilling his role in the invasion. Orochimaru's subordinate, Kabuto Yakushi, instead cast the Temple of Nirvana Technique on the stadium where the finals were being held, putting most present to sleep and signalling the invasion. The Konoha ninja that were present and able to fend off the genjutsu immediately engaged the Oto ninja that had earlier infiltrated the stadium. Gaara and his siblings fled the village with Sasuke and Shino Aburame in pursuit, while Orochimaru discards his guise as the Kazekage and has the Sound Four erect a barrier so no one can interfere with his fight against Hiruzen.

On Konoha's outskirts, Suna and Oto ninja, with help of some of Orochimaru's snakes summons, punched holes in the village's defences, eliminated the border guards, and moved in to the village. All combat-ready ninja sought out the invaders to give the citizens time to escape to the safe area behind the Hokage Monument. Having taken the villagers by surprise the Suna and Oto were able to claim some early victories, in part benefited by the snakes rampaging throughout the village.

As time went on and Konoha's more seasoned ninja came to the village's defence, the tide began to turn against the invaders. Jiraiya stepped in to stop Orochimaru's snakes and most of the Oto ninja at the stadium had been eliminated. Orochimaru, though having managed to bring about Hiruzen's death, had been badly injured by the loss of his arms. This forces him to hold off whatever plans intended to carry out with his mentor's death as the Sound Four escort him to safety with the remaining Otogakure ninja following suit. Realising they have lost the fight with their allies abandoning them, the Sunagakure ninja retreat.

A Battle of Jinchūriki
With Gaara of no use to the invasion, Baki instructed his siblings to take him and retreat, with Sasuke Uchiha and Shino Aburame in pursuit. Naruto Uzumaki, Sakura Haruno, Shikamaru Nara, and Pakkun are later sent to follow Sasuke. While Asuma Sarutobi would later come to Shikamaru's rescue against a group of Oto-nin, Naruto and Sakura find Sasuke as Gaara beats him to an inch of his life upon using his powers as Shukaku's jinchūriki before turning his attention of Naruto. However, unaware that Naruto was also a jinchūriki until after he lost, Gaara underwent a change of perspective as he and his siblings were allowed to leave the Land of Fire without any trouble.

Aftermath
Having realised that something had happened to their Kazekage, Sunagakure scoured the Land of Wind looking for him. They found his body and, realising they had been manipulated into the invasion by Orochimaru, immediately informed Konoha of what had happened. They surrendered to Konoha and offered their apologies, which Konoha accepted. The two villages formed a peace treaty and Sunagakure, inclined to make amends, would thereafter come to Konoha's aid if ever there was need, which proved to be true when Sasuke left Konoha. Sunagakure, despite the casualties they had received in the botched invasion, would benefit greatly from Konoha's influence, adopting the Konoha's structure for an Academy and in later years receiving help when their Fifth Kazekage, Gaara, was kidnapped.

Konoha, though victorious, had suffered heavy losses in the village's defence, chief among them being the loss of their Hokage Hiruzen. Fearing that other parties might prey on them in their weakened state, Konoha earnestly tried to find a new Hokage. At first, the councillors decided that Jiraiya would become the new Hokage. Jiraiya, however, refused the job on the grounds of being was too "irresponsible" and eventually persuaded his former team-mate Tsunade to replace their mentor as the Fifth Hokage as she oversees the village's reconstruction effort. Until Konoha's forces could otherwise be replenished, the surviving ninja were forced to go on more missions than usual and of higher ranks than they were accustomed. For a while the village would be understaffed, to such an extent that when Sasuke Uchiha defected to Orochimaru a team of genin with a new Chunin as the team leader (with some further assistance from some Sunagakure) was the best that could be sent to stop him. By the time that Konoha had stabilised somewhat, they were attacked again.

Trivia

 * As revealed in the Past Arc: The Locus of Konoha, wanting to finish what their comrade began, a pair of Kumogakure ninja abducted Hinata Hyūga during the invasion. However, the abduction was stopped by Neji Hyūga before Hiashi Hyūga came to his aid.