It is often assumed that the true slavs are eastern slavs (Russians, Ukrainians, etc) and that Balkan slavs are mixed with the Illyrians and other native peoples. However, Ken Nordvedt's research shows that haplogroup I2a Dinaric is very young and likely expanded from the area just north of the Carpathians in the last 2,000 years. If this is true that would have to mean that most slavs who came to the Balkans were I2a carriers. This would have to mean that the original slavs would have been closely related to Slovenians and Hungarians. As you can see on this genetic map of Europe Balkan slavs are very close to Slovenians, Hungarians, and Czechs: