Complex sentence: Kościuszko proposed that Prince Józef lead the insurrection in Lithuania, where he was demoting the radical and successful leader Jakub Jasiński, but Poniatowski, not wanting to be so far from his uncle who needed him, declined.
Split into simpler sentences: Kościuszko proposed that Prince Józef lead the insurrection in Lithuania, where he was demoting the radical and successful leader Jakub Jasiński. However, Poniatowski not wanting to be so far from his uncle who needed him, declined.