I've been working on a 64-team worldwide Global League, which contains 16 regional divisions of 4 teams. It's pro/rel, too: there are 16 minor leagues of 16 teams each, and the last-place team in each Global division switches places with the appropriate minor-league champion. (For example, if Buenos Aires finishes last in the Global League's Latin American Division, they get relegated in favour of Montevideo, champions of the Latin American League.)
The leagues will feature as many real teams as I can cram in, but several them will be fictitious or only loosely based on real-life teams. (I just hope my computer can handle it all...
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