Due to insistence of Ekreture, human middle powers include

-Gaian Republic: Appalachian space-confederates
-Humankind Empire of Ithica: Civil-war ridden ex-main/great power turned into a middle power. Space!Syria in terms of all the main powers wanting to jump into it and its numerous competing factions 
-Aries Republic: Treacherous banana republic that Bolshevik'd their pro-human royalty and then become neutral/isolationist, leaving the Terran bloc.
-Mallise Trade Entente: [@Skippy O Africa]'s Space!Venetian + East Indies Trading Company capitalists


UNSURE:
-Elgoeran Federation: Not sure if middle or minor power (or even major): Friendly xenophile Naboo

Minor: 
-United Nations of Earth: Stark trek Earth built in the heart of the former Empire. Very small but has significant cultural and religious importance.