Kasparov calls it quits

... from the world championship cycle.

As for unification, I cannot see an avenue to contribute further. For those who saw me as an obstacle, I will be one no longer. I am not giving up on chess. I will compete as well and as long as I am able to play my brand of chess. I will continue to serve chess and those who love our game. I have now held the #1 ranking for 20 years and I will defend my position against any opponent. My only retreat is from the battlefield of chess championship politics.