Something I've seen once, in a Paradox game (Crusader Kings 2) is having a button that simply links to articles in Wikipedia with historical information.
I love this idea! Simplifies things, no need to completely rewrite the same info for the game, so saves time, and most Wikipedia articles are far deeper than any game designer would have time to write.
I understand this might be a headache to implement in terms of code support for URL field and work to collect and test validity of URLs, just think it would be a great idea particularly for turn-based gaming if it saved effort and added depth.
Paradox haven't done this for subsequent titles so there may be issues with the idea, I understand if so.