Dialects of Serbo-Croatian
Kajkavian is spoken in North Croatia, including the capital Zagreb, as well as in a few enclaves in Austria, Hungary, and Romania. Though its speakers are ethnic Croats and Kajkavian is thus generally considered a dialect of Serbo-Croatian, it is closer to neighboring Slovene than it is to Chakavian or Shtokavian. The Kajkavian area of Croatia is bordered on the northwest by Slovene language territory. It is bordered on the east and southeast by Shtokavian dialects roughly along a line that was the former division between Civil Croatia and the Habsburg Military Frontier; in southwest along Kupa and Dobra rivers, it persisted in ancient (medieval) contact with Chakavian dialects.
Serbo-Croatian
The topic of language for writers from Dalmatia and Dubrovnik prior to the 19th century made a distinction only between speakers of Italian or Slavic, since those were the two main groups that inhabited Dalmatian city-states at that time. Whether someone spoke Croatian or Serbian was not an important distinction then, as the two languages were not distinguished by most speakers. This has been used as an argument to state that Croatian literature Croatian per se, but also includes Serbian and other languages that are part of Serbo-Croatian, These facts undermine the Croatian language proponents' argument that modern-day Croatian is based on a language called Old Croatian.