International Mathematical Olympiad Cumulative Results by Country until now (imo-official.org)

Females participation is very low. None of Arab states is among the top 50. From The Middle East, only Iran appears in the top 20 countries (12th).

USSR and Russia are split for some reason there, cumulative number is noticeably higher.

Same goes for other countries - Yugoslavia, Czechoslovakia, etc.

What a mess honestly :D Same people, different brands.