Now that someone talked about the immigrants, I do not recall receiving them often in my American or Canadian games, making their abilities pretty useless. Speaking of Canada, something that would make it more historical would be if it started its games as a vassal of England, as Canada was not independent from Great Britain until 1931.
I know the UHVs I will talk about can be achieved with good planning, but for the sake of historicity, I feel like Germany's, Japan's and France's conquest UHVs deadlines should be extended.
For example, Germany's and Japan's should be extended to either 1945 or 1950, and France's to somewhere between 1815 and 1830. And if that happens, a new UHV area should be added for balance, maybe Spain or the Balkans for Germany, Polynesia or Australia for Japan, and either 50% of Europe or a little percentage of Africa and Asia for France. I also feel like many control UHVs are bugged, like those of Iran, Turkey, Japan, and Colombia, since they require you to either own the entire land or be the only city owner besides independents, as they are supposed to require you owning more cities in the area than anyone.
Japan's and Germany's third UHVs are something that deserves mixed feelings. For one part, you get to see the late game, unlike most civs. But in the other hand, it is pretty boring to wait until you finish all technologies, unless you make a Space Race or Diplomatic victory, either of which should be faster to achieve than the UHV.
Maybe they should be changed to either "be the first to enter Future Era", "be the first to research these technologies", "have the highest score by this date or for this number of turns by that date", or "be the most advanced civilization by this date".
Can we extend the Arabian UP to self-founded cities as well? Automatic state religion spread and free temples.
The same for Seljuks.
About time someone made this suggestion.