The easiest way to get rid of minor factions as a Craver.

Well at least in my opinion.

The easiest way for the Cravers to consume foreign pops inside their Empire is by using a 1 turn project similar to Exotic Rations. Instead of converting pop into manpower, this project could convert foreign pop into new Cravers or food.

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OR

This is also a fix for the extreme unhappiness problems Cravers currently have to deal with.

Just my 2 

EDIT: I'm more inclined to support the second example as the one best fitting the Cravers.

Meaning, consuming minor factions yields you a large amount of  to go for the next pop growth (preferably Craver if timed right)

Also, I think it is fair to say that consuming a minor faction this way, means you lose the bonus traits that comes with said faction.

This way the Cravers can pick and choose which minor faction suits their playstyle and let them live alongside them. The others can be fodder.