Interzonal

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Interzonal chess tournaments were tournaments organized by FIDE, the World Chess Federation. They were a stage in the World Chess Championship cycle. Basically, the plan was that the cycle would last three years. In the first year, every FIDE member nation would hold a national championship. The top players would qualify to the Zonal tournament. The world was divided into zones. Large countries such as the USSR and the United States had their own zone. Smaller countries would be grouped into a zone with many countries. For example, all of South and Central America combined was originally just one zone. There were originally no Asian or African zones, because there were no countries in those continents that were members of FIDE.

The top players in each Zonal tournament would come together and play in the Interzonal tournament. Typically, the Interzonal tournament would have about 24 players. The top placegetters (e.g. the top six in 1958) would qualify to the Candidates Tournament, which would take place the following year. They would be joined in the Candidates by the loser of the previous candidates final and the loser of the previous world championship match. The winner of the Candidates tournament would play a 24 game match with the World Champion the following year.

To illustrate, in 1957 the US Championship served as a Zonal tournament. The top three, Bobby Fischer, Samuel Reshevsky, and James Sherwin qualified to the Interzonal Tournament that was held in Portorož in 1958. The top six at Portorož (Mikhail Tal, Svetozar Gligorić, Tigran Petrosian, Pál Benkő, Friðrik Ólafsson and Bobby Fischer) qualified to the Candidates tournament. They were joined by Vasily Smyslov and Paul Keres who had been the top two at the 1956 Candidates tournament. Those eight played four games each against each other in the 1959 Candidates tournament. The winner was Mikhail Tal, who then played Mikhail Botvinnik a match for the world chess championship in 1960.

Thus, Interzonal tournaments were held every three years from 1948 until 1993. However, by 1972, the system was becoming unwieldy. There were far too many top level players and the cost of staging these events had become too great. Also, new countries were joining, especially in Asia. China, India, Indonesia and the Philippines started producing top level grandmasters where there had been none before. Even Africa was demanding two zones. It was not practical to put all the top players in a round robin tournament. So in 1973 the system was changed to two Interzonals (with usually the first three in each qualifying for the Candidates), then in 1982 it changed again to three Interzonal tournaments. Further increases led to the Interzonal being staged as a single Swiss system tournament in 1990 and 1993.

The last FIDE Interzonal was Biel 1993, won by Boris Gelfand. The short-lived Professional Chess Association also held one Interzonal, in 1993.