The ‘seventeen Netherlands’ owed their existence entirely to the energies of their rulers. Until 1548 when this hotchpot of duchies, counties and lordships was united in the Burgundian circle of the Empire, the boundaries of the Low Countries had expanded or contracted according to the military and diplomatic fortunes of their princes: there was nothing natural or inevitable about them. Charles V had, for example, threatened to annexe the prince-bishopric of Münster in 1534–5, as he had added Utrecht only a few years earlier. Nor can the incorporation of the duchy of Gelre in 1543 be considered the outcome of an ineluctable historical process. Since the late fifteenth century the rulers in the Low Countries had sought to assert their control over the duchy. But there had been times when it seemed as though Gelre, which looked Januslike both up and down the Rhine, might, in combination with Jülich and Cleves, have constructed a formidable anti-Habsburg constellation into whose orbit a large part of the northern Netherlands would be drawn.

Writing to Wolsey from Bergen op Zoom in 1527 the English ambassador described the Low Countries as being in grave peril from heresy, ‘for yf ther be tre men that speckes, the tweyn keppis Lutter ys openyon’: it was a pardonable exaggeration. Of Luther's immediate popularity in the Netherlands there can be no doubt. In taverns, private houses and on barges the religious issues of the day were hotly debated; from pulpits the new doctrines were championed or denounced, and in public places posters appeared pillorying the mendicants. The succession of placards forbidding the reading, sale or printing of Luther's writings and the increasingly severe penalties prescribed for attendance at conventicles, for harbouring apostate religious and, above all, for spreading heretical notions tell the same tale. Already by 1525 Luther had become a household name in the Netherlands and a new synonym for heretics ‘Luytrianen’ had entered common speech, displacing the older ‘Valdoysen ende Wijclevisten’.