Complex sentence: Before the 1970s Iran did not have a official national league and most teams competed in their local leagues, the most popular of those leagues being the Tehran Local League, which featured teams like Pas Tehran, Persepolis, and Taj.
Split into simpler sentences: Before the 1970s Iran did not have a official national league and most teams competed in their local leagues, the most popular of those leagues being the Tehran Local League. Which featured teams like Pas Tehran, Persepolis, and Taj.