They also developed a new approach to siege warfare, assembling an impressive train of siege artillery, taking the offensive in 1591. Already in 1590 Breda was recaptured with a ruse. But the next year Maurice used his much enlarged army with newly developed transportation methods using rivercraft, to sweep the IJssel-river valley, capturing Zutphen and Deventer; then invade the Ommelanden in Groningen, capturing all Spanish forts; and ending the campaign with the conquest of Hulst in Flanders and Nijmegen in Gelderland. In one fell swoop this transformed the eastern part of the Netherlands, which had hitherto been in Parma's hands. The next year Maurice joined his cousin William Louis in taking Steenwijk and the formidable fortress of Coevorden. Drenthe was now brought under control of the States-General.