I made a quiz that covers every capital that changed in the 20th and 21st centuries. It includes the flags of dissolved States, because I thought it would be fun to see them while quizzing!
https://www.jetpunk.com/user-quizzes/1750503/20th-century-former-capitals
Like Dimby said, the quiz is pretty long. Perhaps divide it into multiple quizzes? Maybe three or so parts. I know your goal is nominations, however. A quiz with over 100 answers cannot be nominated. Also, your description is long. The idea of the quiz is pretty simple, so you might not need all of that explanation.
Nice quiz!
Part 1
Part 2
Plus an extra flag quiz I made that I think is slightly easier :)
Former Countries of the 21st Century - Flags
Now that its just one column, hopefully that's a lot less cluttered, but they seem like a good size to me...
Part 1
Part 2
Plus an extra flag quiz I made that I think is slightly easier :)
Former Countries of the 21st Century - Flags