This policy of steady but quiet centralisation and industrial development was rudely interrupted by the war of aggression undertaken by Louis XIV. against the Dutch. Frederick William was closely connected with the Dutch by marriage and by trade interests, and was one of the first of European sovereigns to draw the sword in their favour in 1673. Beaten hopelessly in the field by Turenne, he was obliged to withdraw from the struggle six months after he had declared war; but in the next year the increasing difficulties of Louis emboldened him again to enter the field. Louis, however, was prepared for this move, and the presence of 16,000 Brandenburgers on the Rhine was the signal of the advance of Charles XI. with a Swedish army on the road to Berlin. Frederick William at once hastened back to defend his capital, reached the Elbe in June 1675, and, dashing forward his cavalry between the two divisions of the Swedish army, seized Rathenow, and prevented their junction on the Havel. [Sidenote: =Battle of Fehrbellin, 1675.=] To do this he had been forced to leave the bulk of his infantry behind. Nevertheless, with the brilliance of decision which marks a great general, he determined to throw himself with the few troops which he had with him upon the Swedish column, which was retreating from Brandenburg, before they reached the pass of Fehrbellin. Pursuing them by forced marches, he came up with their rear-guard on the 17th of June, and on the 18th forced them to accept battle. The weight of numbers was sadly against him. He had but 6000 men against double the number of his enemies, but the Swedes were dispirited, and the elector, in spite of the advice of his generals, insisted on the attack. The battle was hotly contested, but Frederick William had the better position and the more effective artillery, and by nightfall a counter-charge, promptly delivered, carried destruction into the ranks of the enemy. They broke and fled in complete rout through the pass. The day of Fehrbellin is the first great victory of the power of Brandenburg-Prussia, the first step in the ladder which has led to Sadowa and Sedan. It is also the death-day of the military prestige of the Swedes in Europe. From the battle of Lützen to the battle of Fehrbellin, they had never been defeated except by superior numbers. They were now seen not to be able to hold their own with Brandenburg, for Fehrbellin was no isolated victory. The elector pushed on into Swedish Pomerania, victorious and almost unchallenged,--Wohlgart, Stettin, Stralsund and Greifswald fell successively into his hands. By October 1678 Sweden held not a foot of territory in Pomerania. Had it not been for her potent ally at Paris, the work of Gustavus Adolphus and of Oxenstjerna would have been completely undone long before the close of the century, and Frederick William would have been admittedly the master of the north. [Sidenote: =Treaty of S. Germain en Laye, 1679.=] But Louis XIV. insisted upon