Subject Federations Mod
Subject Federations Mod
Simple mod that lets you create Federations with subject empires. I made this originally for my feudal empire mod, but figured some people may want the ability to do so without the changes to the hegemony federation.
This was intended to form federations with your own subjects, but the game makes no distinction so there are may be some potential downsides.
You can form federations with subject nations of other empires and then use the federation fleet to go to war with their overlord, potentially, as an example.