Complex sentence: The only official Genseiryu organisation prior to 1962 was established by Seiken Shukumine in 1953, but this organisation was dissolved in late 1961 or early 1962, which is also part of the reason for Tosa sensei establishing the Nippon Karate-do Genseiryu Butokukai.
Split into simpler sentences: The only official Genseiryu organisation prior to 1962 was established by Seiken Shukumine in 1953. This organisation was dissolved in late 1961 or early 1962, which is also part of the reason for Tosa sensei to establish the Nippon Karate-do Genseiryu Butokukai.