Vassalage.

[TahamiTsunami]

I'm fairly new to the Civ series so I never played Civ 4, but it sounds like vassalage really made that game shine and hopefully it can make it to Civ 6 in another expansion!

 

[Greywulf]

I'm fairly new to the Civ series so I never played Civ 4, but it sounds like vassalage really made that game shine and hopefully it can make it to Civ 6 in another expansion!

It's the reason why I wanted to go back to playing Civ 4 while I was playing Civ 5.