Groenlo formed a crucial link between the Dutch cities that were members of the Hanseatic League, such as Deventer, Kampen, Zwolle, and Zutphen, and the Holy Roman Empire.

Situated in a difficultly passable region, Groenlo developed extensive fortifications that from the late Middle Ages were constantly improved, so that by 1595 the medieval brick city wall was itself surrounded with moats and bastions and armed with cannons.

Maurice had great difficulty to find enough funds and troops for his plans, whereby the campaign into Twente did not start until 1595, when the siege of Groenlo finally begun.

To answer Stirum's request for help, the 81-year-old general and governor of Antwerp Cristóbal de Mondragón, nicknamed 'the good old Mondragon', was sent to Groenlo, accompanied by 7000 foot soldiers and 1300 cavalry.

Aware that the reinforcement troops led by Mondragón posed a major threat to the campaign, Maurice started to bombard Groenlo on 24 July and ordered its immediate surrender.

After heavy deliberation with William Louis, Maurice discontinued the siege the next day, fearing that the approaching reinforcement troops would attack from the back and surround the Dutch forces.