Complex sentence: Soon afterwards however his forces were defeated by the army of hetman Stanisław Koniecpolski and Sulima was turned over to the Commonwealth by Cossack starshina (elders); he together with several other leaders of his rebellion was executed this year in Warsaw on 12 December that year.
Split into simpler sentences: Soon afterwards however his forces were defeated by the army of hetman Stanisław Koniecpolski and Sulima was turned over to the Commonwealth by Cossack elders or "starshina". Together with several other leaders of his rebellion, Hetman Sulyma was executed that year in Warsaw on 12 December that year.