Why Did Itachi Kill His Clan In Naruto?
The massacre of the Uchiha Clan is one of the most important events in the entire "Naruto" timeline. It serves as the motivation for one of the series' leading characters, Sasuke Uchiha, and leads into one of the franchise's most notorious plot threads as Sasuke forsakes everything in a quest for vengeance. On top of that, it ties deeply into the intricate world of the politics and military of "Naruto." The perpetrator of the incident is famously Sasuke's older brother, Itachi, and the motivation behind the then-teenage Itachi's betrayal remains one of the most memorable and shocking revelations the series had to offer.
So why did Itachi kill his own clan? Well, for much of the series, "Naruto" would have you believe it was for some selfish desire. However, the reality of the situation is far from being so simple. As Sasuke peels back the layers of this disturbing conspiracy over the course of the series, both he and viewers begin seeing its participants in a new light. Not only is Itachi more than just a murderer, he might actually be one of the good guys.
To understand the Uchiha Incident, we have to go way back
One of the most interesting things about "Naruto" is how it starts as a relatively small show about good ninjas fighting bad ninjas and expands to become a delicate web of political and interpersonal relationships that paint a picture of the Shinobi world. The Uchiha Incident, as it is called, occurred as a result of generations of dispute between the Uchiha Clan and the rest of the Village Hidden in the Leaves. This is especially true with the Senju Clan, who co-founded the Village with the Uchiha but still comprised a large amount of its leadership. At the time of the Uchiha Incident, all four Hokage had strong familial or friendly ties in to the Senju.
Despite being one of the Village's founding clans, and the leader of its Military Police, the Village Leaders became suspicious of the Uchiha once more following the Nine-Tailed Fox's attack on the Leaf Village. Their clan ability, the Sharingan, has the potential to control the Fox, and it was not implausible to believe an Uchiha might be behind the attack. Sensing this distrust, Sasuke and Itachi's father, Fugaku, began organizing an Uchiha-led coup of the Leaf Village.
Before the slaughter comes the espionage
This alone recontextualizes Itachi's decision to massacre the Uchiha clan. He wasn't a power-hungry maniac who hated his family. That's just what the ninja tabloids want you to think. No, Itachi's brutal betrayal was enacted under orders. That does not mean, however, that Itachi wanted to do it.
See, as part of Fugaku's coup, Itachi used his position in the Leaf Village's ANBU Black Ops to act as an informant. However, Itachi was actually a Village loyalist, and believed that more conflict between the Uchiha and the Village would only spark another Shinobi World War. He became a double agent, answering primarily to the Village's resident scumbag and ANBU leader, Danzo Shimura.
Unlike Danzo, however, Itachi wasn't too inclined to fight against his own clan. He would rather find a peaceful solution, an opinion he shared with the Third Hokage. Unfortunately, Itachi's attempts to broker peace failed, and after the death of his close friend Shisui, he became convinced that peace was no longer an option.
There is one much more personal reason for Itachi's actions
Even after accepting that the Uchiha coup was inevitable, Itachi wasn't hellbent on fighting them. It wasn't until Danzo offered Itachi the mother of all ultimatums that he agreed to become a villain. He could either die along with the rest of his clan at the hands of the Leaf Village, or he could do the dirty deed himself, sparing only his younger brother, and walk away alive. As we already know, Itachi took this deal.
A lot happens during Itachi's massacre, but the gist is that Itachi performs his duty relentlessly and without mercy. As a shinobi prodigy, Itachi stood as one of the Village's strongest soldiers even as a kid. When he happens upon his parents, the two submit and allow him to kill them. They know why Itachi has agreed to kill his clan, and they are proud of him despite their differences. Sasuke appears, and witnesses the death of his parents before Itachi leaves, encouraging him to get stronger and seek revenge.
Prior to killing his parents, Itachi also encounters a man claiming to be Madara Uchiha. The two men then agree to split the killing up between each other. This partnership then leads Itachi to join Madara's organization, the Akatsuki. For the next few years, Itachi lived on the run as an outcast and a war criminal before Sasuke finally tracked him down for their final confrontation.