Directly in the way of the realisation of the least of these designs, as the Great Elector well knew, lay the hostile powers of Sweden and of Poland. He could not touch Pomerania without encountering the bitter jealousy of Sweden, he could not advance an inch towards the union of east Prussia and Brandenburg without first destroying the integrity of Poland. Over the prostrate bodies of these formidable neighbours lay the only road to his territorial ambition. It was a road beset with difficulties. What chance could the barren ravaged and disunited Brandenburg have in an unequal contest with Sweden, at that time admittedly the first military power in northern Europe? How could the half-starved German peasant withstand the onslaught of the brave though undisciplined masses of Polish cavalry? Frederick William knew that he must wait for a favourable opportunity, and spent the time in anxious preparation. His first care was to transfer the conduct of affairs in the mark from the hands of his father’s minister, Schwartzenburg, who was devoted to the Emperor, to his own, and to reorganise the army under himself. In this he was aided by the death of Schwartzenburg in 1641, and the subsequent revolt of his son and the discontented officers. [Sidenote: =Establishment of his personal authority in Brandenburg and East Prussia, 1641.=] Having thus got at his back a force upon which he could depend he openly broke with the Emperor, and with the full approbation of the diet entered into negotiations with the Swedes for a treaty of neutrality. Then turning his attention to the duchy of east Prussia, where the estates were trying to establish their superiority over him, with a diplomatic skill rarely found in a man of twenty, he succeeded in sowing dissensions between the nobles and the representatives of the towns, who took the lead in opposing his authority. By winning the former over to his side he was able to procure the recognition of his rule from John Casimir, king of Poland, in spite of the protest of the towns, and thus to enter legally upon his sovereignty. [Sidenote: =His withdrawal from the Thirty Years’ War, 1643.=] In 1643 the treaty with Sweden was successfully concluded, and for the rest of the war Brandenburg was practically free from the ravages of the rival armies. The breathing space thus gained was devoted by Frederick William to the reorganisation of the finances and the training of the army, and Brandenburg was in consequence enabled to assert her claims to consideration in the negotiations at Münster and Osnabrück with a force which would have appeared incredible in the days of George William. [Sidenote: =Gains of Brandenburg at the peace of Westphalia, 1648.=] When the peace of Westphalia was finally settled it was found that Brandenburg was given the right of annexing the secularised bishoprics of Magdeburg, Halberstadt, Minden and Camin, and the duchy of eastern Pomerania. [Sidenote: =Occupation