The third war of religion, the war of 1569, in which the Huguenots were defeated in the historic battles of Jarnac and Moncontour, had been so devastating that the government lost the disposition to go on fighting, and counsels of moderation prevailed. Coligny, summoned to advise, was listened to with attention, and a marriage was decided on between the king's sister, Margaret of Valois, and Henry of Bourbon, the young King of Navarre, whose birthright made him the head of the Protestant interest. Before the wedding was celebrated a change occurred in the European situation which profoundly affected the policy of France. The revolt broke out in the Netherlands, the real revolt, which was not the work of Belgian nobles, but of the Water Beggars, who took advantage of the maritime configuration, and accomplished the deliverance of the northern provinces. This was Coligny's opportunity. It was the manifest policy of France to intervene, now that the conflict was a serious one, and to rectify the frontier along the line of peril, by which the capital was exposed to attack. What could not have been attempted while Alva held the provinces in subjection, was possible now that his power was shaken to its foundation. England was an obstacle, because England preferred Spanish masters in the Low Countries to French; but it was possible to negotiate compensation with Elizabeth; and Charles IX, under pressure from Coligny, concluded a treaty with her. He also decided that a Protestant force should join the Flemish insurgents in their operations against the Duke of Alva. If they succeeded, their success was to be followed up, and the merit of the expected conquest would be theirs. Conciliation and peace at home would be purchased by victories over the Spaniard. If they failed, they would be disavowed. Accordingly, in July 1572, an expedition under Genlis went to the relief of Mons, and was betrayed and defeated. The Huguenots had had their opportunity and had made nothing of it. The perfidy of the French government was detected, and the king, in his embarrassment, denounced the invaders, and urged Alva to make short work with prisoners. At the same time, he did not give up the scheme that had begun so badly, the scheme for the conquest of Flanders by a forlorn hope of Huguenots.