"Moldavia" = the historic principality, 1346–1859 AD.
"Moldova" = the N-E region in Romania and also the independent country of Moldova.
Both have the name origin in the Moldova River -> Moldovan (in English). The correct way of referring to someone, in English, from both the region and the independent country is Moldovan, thus the culture is also called Moldovan, not Moldavian. Moldavia for the country is correct and it is used in English to differentiate between the old country and the new post-Soviet state of Moldova.
I understand the game isn't about historical accuracy as much as people having fun and having a broad idea about what's going on, so I'll leave it up to you as by that point in time the people themselves were all "Vlahs" regardless of the region anyway.
