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Disputes occasionally resulted in full-scale conflict like the 1583 to 1588 Cologne War, caused when its ruler converted to Calvinism. -
When the Imperial Diet opened in February 1608, both Lutherans and Calvinists sought re-confirmation of the Augsburg settlement. In return, the Habsburg heir Archduke Ferdinand required the immediate restoration of any property taken from the Catholic Church since 1555, rather than the previous practice whereby each case was assessed separately. By threatening all Protestants, his demand paralysed the diet, and removed the perception of imperial neutrality.