First and 9th one is the branch of 7th (history and anime oriented server). 6th is a branch of 8th (pebble). 3th and 4th are branches of 5th (kaisserreich, a mod).
2th might be the most unique one. Under 9th is the server of ulletical, a youtuber friend, under that, my server. Under that, bridge discord, anime.se discord, gamedev.se discord, mariomarathon discord.