Agreed. But US also deserves to get such a UA reflecting the crimes they have done in the last century.
Like every other civ on the planet is so spotless as to avoid a similar fate? :X
But I know Firaxis won't do that.
There are probably more reasons for not focusing on the dark side of various civilizations than you seem to ascribe to them.
For one, most folks buying the game are Western, which is why it's not good to jab too heavily at them. Have to play to your audience, after all.
Second, yeah, there's some bias.
Third, it's pretty much not as big a part of the civilization in both the public mind and actuality as to merit inclusion in the game's limited number of uniques. Like it or not, whatever single defining basic aspect of the American civilization historians come up with will most likely not be "Financed rebellions to install favorable governments."
however Mongols & Aztecs terrorized their surrounding area.
Sacrificing folks and ripping out their heart would certainly inspire terror in me.
Also, Mongols were pretty outrageously brutal when resisted. Not a lot of people who said "No" to the Mongols got away with their homes still standing... 'cept for the Mamaelukes, I guess. When the primary reason you get into Civ is because you embarked on a spree of nearly nonstop conquest, there's not much left to say.
But anyhow, whatever else the U.S. done, it doesn't have the conquer-and-demand-tribute/raze thing going on, nor a state religion built around sacrificing folks to the sun god. Lots of nations have skeletons in their closets, some just have their skeletons closer to the heart than others.
Well, that was a long drift off track.
I agree that the Inca UA will probably involve a bonus to hill farms... maybe something on roads might work too, though. They loved their roads, those Incans. Don't know a whole lot else about the Incan Empire, so I'm going to keep my head down around that.
Spain apparently has the Tercio confirmed, so no question there. Conquistadors sound about right for another UU. UA? Hmm... Maybe something along the lines of extra gold from trade routes from conquered cities? Want to say it'd work for overseas cities only like the actual Spanish Empire, but that probably wouldn't be very good. Maybe a bonus from conquered cities and an extra bonus from overseas cities.