Complex sentence: In contrast, by the 1780s the Austrian Franz Joseph Sulzer had already rejected any form of continuity north of the Danube, and instead proposed a 13th-century migration from the Balkans.
Split into simpler sentences: In contrast, the Austrian Franz Joseph Sulzer had already in the 1780s rejected any form of continuity north of the Danube. Instead he proposed a 13th-century migration from the Balkans.