Itachi soon joined forces with Madara in the massacre of the Uchiha clan, sparing his younger brother, Sasuke Uchiha. Knowing that the blindness brought on by possessing the Mangekyo Sharingan could only be cured by taking the eyes of one's sibling, Itachi spared Sasuke so he could someday take his brother's eyes. Hoping that Sasuke might obtain his own Mangekyo Sharingan by then, Itachi encouraged his younger brother to live hating him and striving to avenge the clan.