It really is all in the name. What else does an overlord do, than lord over his subjects? In the case of Steallris though, those number in the billions, with vassals being planets rather than countries.
Previously in Stellaris, subjugation was rarely a more compelling option than simple conquest and being subjugated often essentially meant a permanent decline of your empire and a “Game Over” screen in your near future. Subjects did not offer sufficient benefits nor had the freedoms necessary to be enjoyable to play.
The Scion origin from Federations was somewhat of an exception with most of the restrictions on both subjects and overlord being waived for them, but the developers say that they felt that, while the system was good, it could be even better. It would also be better if the Scion could work within the rules rather than being an exception, and an anomaly.
Now, both the overlord and subject will be able to propose alterations of the exact terms of their vassalization contract if it’s a contract with another “regular empire”. Those such as the Khan, Awakened Empires, and others, do not haggle about the terms of their minions.
Paradox Interactive
Subject contracts start with a “preset”. These are the basic subjugation types that you know from before, plus a few new ones, such as Vassal, Subsidiary, Tributary, Protectorate, Bulwark, and so on. Presets have a list of default terms and can have additional unique effects tied to them, like how Protectorates gain a massive bonus to research until they catch up to their overlord.
