Official world champions (1886-1993) Apparently, the first time the expression “the world championship match” was used in the contract about the match between Wilhelm Steinitz and Johannes Zukertort. From that moment, decided to count the official title of world chess champion “. What is the difference between casino games and chess? When you play casino game you loose along time. With chess it depends on your and your partner skills. However, before 1948 matches were held without any system: the champion himself defined his rival, the format of the match and the time of the meeting. In 1948, two years after the sudden death of Alexander Alekhine, who left the world without a chess king, FIDE organized a match-tournament five of the strongest grandmasters of the time, which defined the new champion. Free chess website ChessZone  covers all these history. Since then and until 1993 FIDE full control of the process of drawing the title of world champion. Champion had the duty to defend his title every three years in a match with the winner pretendentskogo cycle. In the case of a loss he was entitled to a rematch. Mikhail Botvinnik had used it successfully twice after defeats against Vassily Smyslov and Mikhail Tal. However, in 1963, when Botvinnik lost to Tigran Petrosian, this right was abolished, and start from scratch Botvinnik did not want to. In 1975, Robert Fischer, did not defend his title (after FIDE refused to change some of the conditions of the match), and he went to the winner pretendentskogo cycle Anatoly Karpov.
You could try these:

Useful links: