The main selling point of Humankind is a new way how you build your civilisation (culture), as through different eras you will be able to develop your culture by combining various civilisation types based on historical societies, which will give you both bonuses and penalties that come with that culture, allowing for an enormous number of unique cultures.
As with any 4X strategy game, one of the main things you will do throughout the game is conquering other Empires.
Humankind Vassal Empires explained
If an Empire surrenders in a war with you, one of the options is to make that Empire your Vassal.
When presented with the Surrender Terms, you can choose for the defeated Empire to become a Vassal of your Empire.
By choosing that option, the two Empires are now entering the Liege-Vassal relationship or simply put - Vassalage.
What are the immediate positive things you will see when you subordinate an Empire?
- A Vassal is obligated to pay tribute to you, an X amount of money per turn.
- The Diplomatic States, State Religion, and Treaties of your Vassals are controlled by you.
- Any Treaty which you successfully negotiate with other Empires will be applied to Vassals as well.
- You will get access to all the Strategic and Luxury resources of your Vassal Empires.
Aside from these, it's also important to note that you will receive almost all of the benefits of a conquered Empire without spending resources on war, which can be quite costly.
The Vassalage status will also spare cities in a Vassal Empire from destruction, which is good both for you and the Vassal Empire.
So, what are the downsides of turning an Empire into your Vassal state instead of conquering it? To be honest, in the current version of the game, there are not many negative sides, really.
A number of players are complaining that the Vassalage mechanic "is ruining the game" as it is too easy to make Vassals and maintain that status without any real penalties.
If the conditions are right (which is not a hard thing to achieve), you can force many Empires to surrender and demand the Surrender Terms which they are forced to accept.
There is a chance for the Vassal Empires to demand their freedom from the Liege, but that rarely happens as conditions for that are hardly achievable. You don't need to actively demonstrate force or even have up-to-date units in Vassal states.
One thing which might be considered a negative is that you also share resources with your Vassals, but that's negligible as huge benefits offset any potential losses in that regard.
The only real downside is that you are obliged to go to war if any Empire attacks your Vassals, which might create some unwanted and unplanned expenses.
Hopefully, developer Amplitude Studios will listen to player feedback and make some balance changes for this mechanic, so that it will be harder to make Vassals and even harder to control them. At its core the Vassalage mechanic is interesting, but currently, it makes things too easy for players.