Behind the shadows the real reason why Itachi killed the Uchiha Clan
The Uchiha along with the Senju were the most powerful clan in Konoha. In fact so powerful that they were feared across nations. Tobirama, the second Hokage knew of Uchiha’s hate and the activation of Mangekyo Sharingan. He even feared a Madara Uchiha like occurence in some time hence he made the Uchiha the police force of the village and sent them to a corner. With time, the surveillance on the Uchiha increased thanks to Danzo’s stupidity. He used his authority to do all kinds of shit. This angered the Uchiha quite a bit and they decided to rebel which ultimately lead to the massacre of the clan leaving only 3 survivors Itachi, obito and Sasuke. Among whom, Itachi and Obito were ultimately killed and Sasuke went through a rough patch like no other not knowing what to do in life and ultimately taking on Naruto only to lose to him.
But that is the dark history of the Uchiha, in which itachi played a key role.