In 1598, the Spanish under Francisco Mendoza retook Rheinberg and Meurs in a campaign known as the "Spanish winter of 1598-99". Mendoza then attempted to take Bommelerwaard island but the Dutch and English under Maurice thwarted the attempt and defeated him at Zaltbommel. Mendoza retreated from the area and the defeat resulted in chaos in the Spanish armymutinies took place and many deserted. The following year the Dutch senate led by Johan van Oldenbarneveldt saw the chaos in the Spanish army and decided the time was ripe for a focal point of the war to be concentrated in Catholic Flanders. Despite a bitter dispute between Maurice and van Oldenbarneveldt, the Dutch and a sizeable contingent of the English Army under Francis Vere reluctantly agreed. They used Ostend (still in Dutch hands) as a base to invade Flanders. Their aim was to conquer the privateer stronghold city of Dunkirk. In 1600 they advanced toward Dunkirk and in a pitched battle the Anglo-Dutch inflicted a rare defeat on the Tercio-led Spanish army at the Battle of Nieuwpoort in which the English played a major part. Dunkirk was never attempted however as disputes in the Dutch command meant that taking Spanish-occupied cities in the rest of the Republic took priority. Maurice's force thus withdrew leaving Vere to command Ostend in the face of an imminent Spanish siege.