It was a bitter lesson to the Great Elector, but ever patient and ever trustful of his own diplomatic skill, he continued his policy and awaited a more favourable opportunity, but for the present he had to submit to the inevitable. The Brandenburg contingent marched with Charles X. and the Swedish army to Warsaw, and did their share in the winning of the great three days’ battle in July 1656, which placed Poland at the feet of the Swedes. But the victory of Charles X. was, as is so often the case, the beginning of his difficulties. It was always easy to defeat a Polish army, it was almost impossible to reduce the country to submission. The intrigues of the Great Elector began to bear fruit. [Sidenote: =Coalition against Sweden.=] While Charles was planning the pursuit of John Casimir into the recesses of the forests of Galicia, the king of Denmark was preparing to invade Sweden itself, the Russians declared war, and a horde of Tartars and Lithuanians poured into east Prussia. Charles X. found himself in the middle of a hostile country, with a doubtful ally, surrounded by a host of enemies. Frederick William insisted on an immediate return to defend east Prussia from the invaders. Charles could not resist so plausible a demand. [Sidenote: =Treaty of Labiau. Ackowledgment of the independence of East Prussia by Sweden, 1656.=] With a heavy heart he retired from the scene of his victory into west Prussia, where he took ship for Denmark, having first done what he could to retain Frederick William in his enforced alliance by recognising the independence of east Prussia in the treaty of Labiau, signed in November 1656. Directly his back was turned, the Great Elector threw off the mask, and offered his friendship and assistance to John Casimir, if only he would follow the example of Sweden, and release east Prussia from all claims of feudal vassalage. [Sidenote: =Treaty of Wehlau. Acknowledgment of the independence of East Prussia by Poland, 1657.=] As long as he obtained his independence, Frederick William did not trouble about the honesty of the transaction. John Casimir accepted the terms. By the treaty of Wehlau, concluded in September 1657, the Great Elector cynically reversed the treaty of Labiau, made only ten months before, became the ally of Poland and the enemy of Sweden, and received as the reward of his dissimulation, the recognition of the independence of east Prussia by his legitimate suzerain.