Complex sentence: The battle ended with a Swedish surrender mainly due to: low-moraled German mercenaries in Swedish service who started a mutiny in which they negotiated with the Polish command without Streiffs knowledge and prepared for a side switch to join the Polish army.
Split into simpler sentences: The battle ended with a Swedish surrender mainly due to low-morale of German mercenaries in Swedish service. These troops started a mutiny and negotiated with the Polish command without Streiffs knowledge and prepared to switch sides to join the Polish army.