Sickingen had been induced by Charles V to assist him in an abortive attempt to invade France in 1521, from which campaign he had returned without much benefit either material or moral, save that Charles was left heavily in his debt. The accumulated hatred of generations for the priesthood had made Sickingen a willing instrument in the hands of the reforming party, and believing that Charles now lay to some extent in his power, he considered the moment opportune for putting his long-cherished scheme into operation for reforming the Constitution of the empire. This reformation consisted, as was to be expected, in placing his own order on a firm footing, and of effectually curbing the power of the other estates, especially that of the prelates. Sickingen wished to make the Emperor and the lower nobility the decisive factors in his new scheme of things political. The Emperor, it so happened, was for the moment away in Spain, and Sickingen's colleagues of the knightly order were becoming clamorous at the unworthy position into which they found themselves rapidly being driven. The feudal exactions of their princely lieges had reached a point which passed all endurance, and since they were practically powerless in the Reichstags, no outlet was left for their discontent save by open revolt. Impelled not less by his own inclinations than by the pressure of his companions, foremost among whom was Hutten, Sickingen decided at once to open the campaign. Hutten, it would appear, attempted to enter into negotiations for the co-operation of the towns and of the peasants. So far as can be seen, Strassburg and one or two other Imperial cities returned favourable answers; but the precise measure of Hutten's success cannot be ascertained, owing to the fact that all the documents relating to the matter perished in the destruction of Sickingen's Castle of Ebernburg. It should be premised that on August 13th, previous to this declaration of war, a "Brotherly Convention" had been signed by a number of the knights, by which Sickingen was appointed their captain, and they bound themselves to submit to no jurisdiction save their own, and pledged themselves to mutual aid in war in case of hostilities against any one of their number. Through this "Treaty of Landau," Sickingen had it in his power to assemble a considerable force at a moment's notice. Consequently, a few days after the issue of the above manifesto, on August 27, 1522, Sickingen was able to start from the Castle of Ebernburg with an army of 5,000 foot and 1,500 knights, besides artillery, in the full confidence that he was about to destroy the position of the Palatine prince-prelate and raise himself without delay to the chief power on the Rhine.