Complex sentence: In early 1601 Albert of Austria had begun to besiege the city of Ostend and at the same time States General at this time demanded that Maurice should march to relieve the city; to take on the besiegers.
Split into simpler sentences: In early 1601 Albert of Austria had begun to besiege the city of Ostend. The States General at this time demanded that Maurice should march to relieve the city; to take on the besiegers.