It is worth recalling that after the AVRO tournament in 1938, in which eight of the strongest players of the world participated, another attempt was made to settle the question concerning matches for the world championship. At a meeting of the participants a proposal was made to organize "the club of eight" which was to be entitled to fix regulations for the world championship, any member of the club being entitled to play a match with the world champion and admittance to the club being decided by a vote among club members. In other words, it was proposed to replace the personal dictatorship of the world champion by a dictatorship of "the eight", the right to play a match with the champion not being won by eliminatory competitions, but by winning the favors of the all-powerful members of the club. At the request of the participants in the AVRO tournament, the grandmasters R.Fine and M.Euwe some time later elaborated a project for "regulations", but the Second World War suspended for the time the decision about this question. - M. Botvinnik, 'On the World Championship', FIDE Review 1956
In the same essay, Botvinnik discussed the various rules that governed match play for the title in the post-WWII years.
The eight participants at AVRO were Alekhine, Botvinnik, Capablanca, Euwe, Fine, Flohr, Keres, and Reshevsky. Capablanca died during the war, Alekhine shortly after the war ended. The six surviving players were invited to the 1948 FIDE World Championship Title Tournament, with Smyslov replacing Flohr.