Complex sentence: Many of these became instrumental in the foundation of the HEMA Alliance, the structure of which was directly influenced by their experience in ARMA, though some assert that ARMA's membership was quickly restored to its previous level.
Split into simpler sentences: Many of these became instrumental in the foundation of the HEMA Alliance, the structure of which was directly influenced by their experience in ARMA. Additionally, some assert that ARMA's membership was quickly restored to its previous level.