Complex sentence: Stephen returned from Poland and defeated the invaders with Polish assistance at Catlabuga Lake in November and at Șcheia in March 1486, but he could not recapture Chilia and Cetatea Albă.
Split into simpler sentences: Stephen returned from Poland and defeated the invaders with Polish assistance at Catlabuga Lake in November. He again defeated the Ottomans at Șcheia in March 1486, but could not recapture Chilia and Cetatea Albă.