I'm not so sure where you are in the manga but . . .
Sasuke and the resurrected Itachi were battling Kabuto together. They defeated him but only with Itachi sacrificing himself thereby declaring his will to protect Konoha even if doing so cost him his life. Sasuke, however hating Konoha for all the suffering it put Itachi through, retaliates;
(To Itachi) "I guess anything I say now would be pointless… When I saw you… I decided to follow you here to confirm whether or not what Danzō and Tobi told me was true or not. But that wasn't the only reason… When I'm with you I remember the way it used to be. I remember time spent with the brother that I looked up to… that I loved. That's why… The closer I get to you… The more I'm able to recall what those those days felt like… And the more I'm able to understand you.The more I'm able to hate Konoha for the suffering they put you through. In fact, it's becoming even stronger than before. I do understand what you want me to do. It's probably because you're my older brother that you feel the need to put me on the right path. But it's probably because I'm your younger brother that I'll never stop, no matter what you say. As you'll always exist to protect the village… so will I to destroy it. Goodbye… brother."
Itachi returns to the afterlife and soon after that Sasuke meets up with Suigetsu and Juugo. Together they come across Anko and Sasuke uses her curse mark to summon Orochimaru.
Orochimaru declares that he has no interest in the on-going war and that he is to weak to try to take over Sasuke's body.
Orochimaru then guides Sasuke to some place they both seemed to know quite well . . . .
You could visit narutospot.net to read the manga or visit Sasuke's Narutopedia page
