Mary of Hungary, Charles V's sister, who was chosen by him to succeed Margaret of Austria, did not enjoy the independence of her predecessor. She confined herself to executing faithfully the instructions she received, even at the cost of her popularity. The emperor installed her at Brussels in 1531. He had been previously absolved by the pope from his oath at the time of the Joyous Entry of Brabant, and proceeded to strengthen the Central Government by the creation of three collateral Councils and the proclamation of a Perpetual Edict giving a common constitution to all the provinces of the Netherlands. After his departure, Mary was at once confronted with military difficulties. Christian II, no longer restrained by Margaret, had concentrated troops in Holland in order to attack Frederick of Holstein. His violation of the neutrality of the Netherlands caused reprisals against the Dutch merchant fleet, but Antwerp and Brussels refused to wage war in its defence. Thanks to the death of Holstein, Mary succeeded in negotiating a satisfactory treaty with Denmark at Ghent (1533). The resistance of the States General and the towns to the warlike policy of Charles caused further trouble when, in 1536, hostilities between the two rivals were resumed. In vain did Mary endeavour to obtain the neutralization of the Low Countries, in vain did she offer her resignation. In spite of serious reverses, the emperor maintained his attitude, while the States General declared "that they were not rich enough to help him to conquer France and Italy." Their resistance was only overborne when, in 1537, the French armies invaded the Low Countries. Under this threat, they voted the taxes and organized resistance. The French king, disappointed in his hopes, signed the truce of Nice, 1538.