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For example, s good player will improve his performance if he is playing in England. While the same player will probably stagnate if he plays football in some minor league.
From what I can see, the current trend (a very recent one, I'd say) is for European players to get contracts with less known leagues around the world (one example is that of Cristiano Ronaldo playing for Al Nassr), and at the same time players from AFC and CAF participating in the top leagues such as Serie A and the English Premier League. European leagues always had Asian and African players to a certain degree. But this trend has really accelerated during the last few years, which is helping the Asian and African national teams in a big way.