Early on in the Naruto anime, Sasuke Uchiha made one thing clear: He needed to grow as strong as possible, so he could destroy his own older brother, Itachi. Sasuke's relationship with Itachi had been one of deep brotherly love and admiration, with little Sasuke pining for more time to spend with his hero. But then Itachi committed an unforgivable act when he massacred the Hidden Leaf Village's entire Uchiha clan, sparing only Sasuke.
Source：https://www.cbr.com/naruto-why-itachi-killed-uchiha-family/
