The question is simple, but the reason might be less so.
In the Tribute Policy, it describes the acquiring of new tiles as scaling with Era.
However, when actually demanding tribute from a city-state, there is no such description there saying that it does scale with era. However - demanding tribute on a city-state most definitely DOES scale with era.
What's happened in the current game: I noticed that my tribute demands were providing higher yields than I anticipated, even for Mongolia. What I did with at least 1 city-state was annihilate all its troops, burn down all its stuff, and choke the city so it doesn't even have a military unit in it. With enough troops surrounding the city, I'm able to demand tribute every single turn for 100%. This is increasing my Culture yields something like eight-fold (and it's a Faith city-state...). I'm not sure if this behaviour is intentional or not, but boy is it great!
In the Tribute Policy, it describes the acquiring of new tiles as scaling with Era.
However, when actually demanding tribute from a city-state, there is no such description there saying that it does scale with era. However - demanding tribute on a city-state most definitely DOES scale with era.
What's happened in the current game: I noticed that my tribute demands were providing higher yields than I anticipated, even for Mongolia. What I did with at least 1 city-state was annihilate all its troops, burn down all its stuff, and choke the city so it doesn't even have a military unit in it. With enough troops surrounding the city, I'm able to demand tribute every single turn for 100%. This is increasing my Culture yields something like eight-fold (and it's a Faith city-state...). I'm not sure if this behaviour is intentional or not, but boy is it great!