[Cainehill]

Yep, almost any nation can cast the spell - but certain nations can use it more effectively. For example, Ulm with the lich pretender can have a 27 protection, ethereal, life-stealing black servant out by turn 5 or 6 ( loaded with full black steel armor, helm, and shield ).

Likewise, Machaka has an earth income, albeit it can't equip a BS as quickly - but it has mages with earth and death, so while it may need to find some sites first, it can produce them without needing a pretender to do it.

By the mid-to-late game, these mini-thugs aren't worth as much, which is why you then see spectres kitted out with magic being used as thugs. But the black servants can be very useful for early expansion against indies & the AI, and even as a surprise against human players.