Well done! I would recommend putting a missing countries/answers button, but given the number of answers in the quiz, it likely wouldn't be of any help unless someone hold had a handful of countries left.
This is a really cool quiz series! Just wondering: what sources do you use for searching the countries? I can barely find some of them even with their names :)
Mostly through YouTube videos and maps on Wikipedia regarding specific regions. It's pretty much a fact that a lot of these nations are pretty obscure and thus would have a lack of any information online, especially the Americas and Sub-Saharan Africa during this time period.
100% GG