This chapter examines the wars that broke out in the Netherlands, at least partly because of reformation, during the final third of the sixteenth century. Militant Reformed Protestantism established itself in the Low Countries, especially in the western provinces, by the early 1560s. In 1566, the “wonderyear,” political and religious protest erupted into the open, as nobles protested Habsburg religious policy and Reformed militants sacked churches in an iconoclastic fury. This in turn caused Philip II to install a military regime, led by the Duke of Alba, in order to suppress rebellion and heresy. In 1572 the rebels won territory in the north, and by 1580 gained control of the northwestern half of the region, where Reformed militants instituted a revolutionary reformation to root out Catholicism. Sectarianism in turn caused a breakdown of the rebel alliance, and by the mid-1580s the Habsburg had successfully retaken most of Flanders and Brabant. By 1590 a military stalemate had bifurcated the Netherlands, with the rebels in control of the seven northern provinces and the Habsburgs in control of the ten southern provinces. Each region would follow its own religious trajectory.