Search as I might, I cannot find casus belli..."Because I want to"

[sarge33rd]

seems an oversight.

 

[MordridBlack]

Ah, then you want to run either an "Evil" empire setup, or assuming you have the Apocalypse DLC, research and build a Colossus

Evil Empires - Fanatic Purifier, Devouring Swarm (Requires Utopia DLC), Determined Exterminator (Requires Synthetic Dawn DLC)

all of these give you an option that is pretty close to "Because I want to"

 

[unbeatable101]

Ah, then you want to run either an "Evil" empire setup, or assuming you have the Apocalypse DLC, research and build a Colossus

Evil Empires - Fanatic Purifier, Devouring Swarm (Requires Utopia DLC), Determined Exterminator (Requires Synthetic Dawn DLC)

all of these give you an option that is pretty close to "Because I want to"

Or just try to vassalize them in your current save.

 

[MordridBlack]

Or just try to vassalize them in your current save.

that requires you to not be evil and for them to view you as vastly superior [either for you to make that demand or for them to ask it of you]

 

[MrFreake_PDX]

seems an oversight.

Make claims on their territory, that grants a CB Or do a humiliation war, which doesn't let you take any territory, but lets you beat them up. Or build a colossus or play a total war empire, which will give you a total war CB, which will let you take all their stuff and make it your stuff

 

[unbeatable101]

seems an oversight.

If you have the apocalypse DLC try this from the wiki

An Empire that owns a Colossus gains the ability to declare Total Wars on other Empires. Similarly, any Empire can declare Total Wars on the Colossus owner. During a Total War, any systems captured by either side will be immediately annexed and the war can only end in the total destruction of either side or a status quo.