You just need slapping down. How on god earth would Obito kill Madara when his left side of his body is crushed. His other eye belongs to Kakashi AND OBITO WAS NOT EVIL AT ALL.To everyone who is wondering how Madara knew Nagato:
In chapter 400, page 9 u can see Madara talking to Itachi meaning Madara lived at the same time as Nagato. That explains how Madara knew Nagato.
Tobi or Obito as I like to call him probably killed Madara and took his right eye.