Complex sentence: The IFW grew rapidly, especially by assimilating several pre-existing wargaming clubs, and aimed to promote interest in wargames of all periods and provided via its newsletters and societies a forum for wargamers to form local groups and share rules.
Split into simpler sentences: The IFW grew rapidly, especially by assimilating several pre-existing wargaming clubs, and aimed to promote interest in wargames of all periods. It provided a forum for wargamers, via its newsletters and societies, which enabled them to form local groups and share rules.