Complex sentence: It was an Imperial State in the Holy Roman Empire, and the Bohemian king was a prince-elector of the empire, who besides Bohemia ruled also the Lands of the Bohemian Crown.
Split into simpler sentences: It was an Imperial State in the Holy Roman Empire, and the Bohemian king was a prince-elector of the empire. The Czech king besides Bohemia ruled also the Lands of the Bohemian Crown.