The relationship of the Netherlands to the Empire was a delicate and important question. Though the Empire was the feudal suzerain of most of the Burgundian provinces, Charles felt far more keenly for his rights as an hereditary, local prince than for the aggrandizement of his Empire, and therefore tried, especially after he had left Austria to his brother Ferdinand, [Sidenote: September 7, 1522] to loosen rather than to strengthen the bond. Even as early as 1512, when the Imperial Diet demanded that the "common penny" be levied in the Netherlands, Charles's council aided and abetted his Burgundian subjects in refusing to pay it. In 1530 the Netherlands, in spite of urgent complaints from the Diet, completely freed itself from imperial jurisdiction in the administration of justice. Matters became still more complicated when Utrecht, Friesland, Groningen and Guelders, formerly belonging to the Westphalian district of the Empire, were annexed by Charles as Burgundian prince. Probably he would not have been able to vindicate these acts of power, had not his victory at Muehlberg [Sidenote: 1547] freed him from the {239} restraints of the imperial constitution. A convention was made at the next Diet of Augsburg, [Sidenote: Convention of June 26, 1548] providing that henceforth the Netherlands should form a separate district, the "Burgundian circle," of the Empire, and that their prince, as such, should be represented in the Diet and in the Imperial Supreme Court. Taxes were so apportioned that in time of peace the Netherlands should contribute to the imperial treasury as much as did two electors, and in time of war as much as three. This treaty nominally added to the Empire two new counties, Flanders and Artois, and it gave the whole Netherlands the benefit of imperial protection. But, though ratified by the States General promptly, the convention remained almost a dead letter, and left the Netherlands virtually autonomous. As long as they were unmolested the Netherlands forgot their union entirely, and when, under the pressure of Spanish rule, they later remembered and tried to profit by it, they found that the Empire had no wish to revive it. [Sidenote: Reformation] The general causes of the religious revolution were the same in the Low Countries as in other lands. The ground was prepared by the mystics of the earlier ages, by the corruption of and hatred for the clergy, and buy the Renaissance. The central situation of the country made it especially open to all currents of European thought. Printing was early introduced from Germany and expanded so rapidly in these years [Sidenote: 1525-55] that no less than fifty new publishing houses were erected. As Antwerp was the most cosmopolitan of cities, so Erasmus was the most nearly the citizen of the world in that era. The great humanist, who did so much to prepare for the Reformation, spent in his native land just those early years of its first appearance when he most favored Luther.