Itachi seeked out madara to help kill his clansmen. this was an agreement so madara wouldn't attack the village if he help itachi kill the clan. itachi did kill uchiha shinsui and gained MS. it is proven and it has no evidence proving otherise. shinsui was the best uchiha next to itachi. the clan knew itachi to be a prodigy but did not know the extent of his power. this can be noted when 3 police officer came to question him about shinsui death and he took them out in 2 or 3 seconds. this is full 3 tome sharingan users. itachi abilities was unrivaled because he killed the best of his clan without a scratch. there was no visible wounds on him the next day. which leads us to believe he is extremely powerful. this was then confirmed by the elder to pick itachi out of all his clan members to carry out the massacar. he was the only one talented and skilled enough to do it. madara couldt kill the entire clan by himself and neither could itachi but together they could. remember this is the uchiha clan. the most formidable and known as a battle clan even a genius was just ordinary before them.
The Konoha Council and Danzo were the ones who told Itachi to kill the Uchiha clan.
He is one of the strongest however Madara Uchiha could be stronger.
Danzo and the Konoha Council ordered him to wipe out the Uchiha Clan, who were planning a coup d'etat against Konoha. He made a deal with Madara Uchiha, who would spare Konoha if Itachi would help him wipe out the Uchiha Clan, who had betrayed Madara earlier. Madara agreed and the two wiped out the entire Uchiha Clan in one night. (With the exception of themselves and Sasuke Uchiha, Itachi's younger brother due to the fact that Itachi could not bring himself to kill his little brother.)
itachi was a spy from d village hidden in d leaves and was ordered 2 because saskes dad was going to start a war..... WRONG, it was a conspiracy. they were afraid it would happend, so Danzo, and the three elders ordered itachi to do it.
Fugaku Uchiha
: Because he loves Sasuke. to make sasuke suffer by knowing there dead and hes alone and making him die slowly by the fact of not being able to kill him Itachi wanted to protect Sasuke. He killed his family, his clan, his lover, but couldn't manage to kill Sasuke. When their battle was over, Itachi passed on his eye techniques to Sasuke so he could be protected against Madara Uchiha's Sharingan. Itachi thought that if he passed on the black flame technique to Sasuke then when Madara showed Sasuke his Sharingan, Madara would be wiped out and never tell Sasuke all the truth. But it failed. Itachi was ordered to kill everyone. But afterwards he threatened the Elders Of Konoha and begged the Third to protect Sasuke. He let Sasuke live on with the goal of revenge to make him appear more powerful. He freed Sasuke of the Curse Seal when he tore Orochimaru's power from him. He lied, killed. threatened, and fought to protect his brother because he loved him. He wouldn't do all of that to just kill him. He couldn't even if he wanted to. That is the true definition of their bond as brothers.
he said that he had an enormous amount of chakra so he could survive for very long
Of course Itachi would be Madara if he had Sasuke's eternal. He could probably still win even without that ability. Itach is a genius after all.
the uchiha were planing a coup d'état on the leaf that is what madara predicted but the three elders planted itachi as a spy to keep the info on them Then itachi was received the mission to kill the entire uchiha clan. itachi kept sasuke alive not to measure his vessel it was because he just couldn't bring himself to kill his little brother.Then he went to the third hokage he told him if you lay one hand on sasuke ill kill you instantly then he left without a word. He was to be considered a traitor due to the assassination. Itachi wanted sasuke to kill him so he could be known to revive his clan but itachi didnt expect sasuke to join orochimaru which his plans were failed but sasuke still kills him then finds out the truth by madara
After Sasuke battled Itachi, it was said by Madara Uchiha, AKA Tobi, that Itachi died on purpose. Madara stated that Itachi wanted to battle Sasuke to finally give him what he wanted. During the battle, Sasuke managed to go up against all of Itachi's Mangekyo Sharingan techniques and stay safe. Towards the end of the battle, Itachi starts to reach out to Sasuke to get his eyes so he could have the Eternal Mangekyo Sharingan to keep from going blind. Itachi used his ultimate jutsu, Susanoo and blocked all of Sasuke's attacks, even though it came with the cost of killing him. When Sasuke was backed into a wall, Itachi simply tapped Sasuke on the forehead and said, "Sorry Sasuke, there won't be a next time" and dropped to the ground. While waking up, he finds Madara and when he sees Madara's Sharingan, Sasuke immediately uses Amaterasu, unlocking his Mangekyo Sharingan.
it was order from konoha ,uchiha was planning war with konoha
Madara uchiha is much stronger than shisuia uchiha seeing that he has a permanant mangekyo sharingan and that he is the clan leader of the uchiha clanSO.madara uchiha could beat up shisui uchiha blindfolded, ha-not really, but madara uchiha could actually beat up shisui uchiha if they had a fightumm actually u would have to remember Shisui's mangekyou had the power of mind control and also he is know as "Shisui the Body Flicker" his speed jutsu menipulation is equall to of what madara uchiha used with his time space jusutu but yet even with that madara was born of a god a tengu a konoha tengu "madara's father" and his mother being a hyuga with the orginalization of the kekkegankai in volume 9 of naruto they speak of how every eye kekkegankai originated with the hyuga wich with these facts prove is true but back to the point thing is i think that they would be at a stand still.p.s. if u want more info look me up on imvu lUchihaShisuil ;D