The crisis came in 1657, the year in which Oliver was raised by Parliament to the constitutional Protectorate. Charles X. having secured a hold on the mouth of the Vistula by his occupation of Western Prussia had naturally become an object of suspicion to Frederick William of Brandenburg--the Great Elector, as he was subsequently styled--who saw with displeasure the growing power of Sweden on the Baltic coast and who was urged by every consideration of policy to secure for himself the strip of land which intervened between part of his own possessions and the sea. Frederick III. of Denmark again, fearing the ultimate loss of his own territory beyond the Sound, took the opportunity of declaring against Charles, and both Brandenburg and Denmark, Protestant as they were, looked for the support of Leopold, who had just succeeded to the Austrian hereditary estates. Leopold, however, instead of hurrying to the assistance of these two States, was held back by purely political interests, and showed little inclination to assist them. Charles X. took the opportunity and led his army through Holstein into Schleswig and Jutland without difficulty, thus gaining possession of the whole of the Continental States of the King of Denmark. The Swedish King had been ready to fool Oliver to the top of his bent. Though he had nothing of the spirit of the crusader, he was quite prepared to gain what advantage he could out of Oliver's enthusiasm. Happily for England, he had rejected the Protector's proposal--made in the spring of 1657--to take over the secularised Archbishopric of Bremen as a security for a loan, the Archbishopric being required by Oliver as a basis for an advance into Germany in an attack upon the German Catholic States, a project far more unwise than the occupation of the Flemish ports, and one which, if it had been carried into effect, would have left little room for Oliver's panegyrists to dwell upon the excellence of his foreign policy. For the remainder of the year Charles was quite ready to discuss the Protestant alliance, if only he were not required to carry it into immediate action. No doubt he would be ready at some future time to attack Austria or any other country if there was anything to be gained by it. For the present he was occupied with his quarrel with Denmark, and till that had been brought to a conclusion, there was nothing else to be done.