Transylvania was a country at the site of OTL north-western Romania.
Originally a part of Hungary, during 1480-1492 the Rum-Seljuks broke Hungary up, leaving only Slovakia and the western third to the king. The center and Croatia were annexed, Transylvania became a tributary.
During 1635-46, the Second French-Seljuk War was fought. In the peace of Györ, Bourbon Hungary acquired Transylvania, plus Croatia, Slavonia, and the Banat.
With the Hungarian Division of 1834, Transylvania became a Russian protectorate.