Complex sentence: Hartknoch's work in the Polish-Lithuanian Commonwealth, Kaunas, and Vilnius awoke his interest in their history, he wrote a comprehensive work on the Commonwealth spanning 300 years, the first of its kind.
Split into simpler sentences: Hartknoch's work in the Polish-Lithuanian Commonwealth, Kaunas, and Vilnius awoke his interest in their history as well. He then wrote a comprehensive work on the Commonwealth spanning 300 years, the first of its kind.