Despite the quality of the Swedish army, Charles was actually rather vulnerable. When he turned north at the end of October, he left Wittenberg in Cracow to control southern Poland with only 3,000 men, apart from those scattered in garrisons across a wide area, supplemented by 2,000 Poles of dubious loyalty. When they abandoned him, Wittenberg was left dangerously exposed. The substantial garrisons in the main cities may have been safe enough, given Polish shortcomings in infantry and artillery, but even here the Swedes were handicapped by the frequently poor fortifications, which meant that towns were easy to take but difficult to hold. The situation was worse in the countryside. In small towns and villages, Swedish garrisons huddled in crumbling medieval castles or did without serious protection altogether. Foragers were vulnerable to ambush by peasants or marauding cavalry. The experience of Hieronymus Christian von Holsten in Lanckorona with 150 men, including only 16 horse, was typical: the town had no defences, so the Swedes withdrew to the protection of the medieval castle at night, but were forced to call for reinforcements in the shape of 50 horse after their vulnerability was underlined when they came across several Swedes in a noble manor who had been murdered cin dastardly fashion’. As the bitterness provoked by Swedish looting and contributions grew, the war escalated into a savage cycle of slaughter and retribution.
The Poles were fighting an enemy who had learned much since the 1620s. The importance of cavalry was fully recognised: the Swedish invading force in July 1655, contained 14,000 horse (40 per cent) to 1,250 dragoons and 20,050 foot. Recruitment subsequently concentrated on cavalry, with the raising of thirty-eight cavalry regiments (13,888 men), six dragoon regiments (3,264) and only seven of foot (6,048), increasing cavalry units by 75 per cent compared to 35 per cent for infantry units. With such an army Charles was able to fight a mobile war, though such a strategy was fraught with danger. In early 1656 Charles set off in pursuit of Czarniecki’s force of 2,400 with about 11,000 horse, defeating him at Golab before advancing on Lwów. He received a sharp lesson in the realities of eastern warfare. Zamosc’s modern fortifications enabled Jan Zamoyski politely to decline an invitation to surrender, and although Charles had been joined by 3,000 infantry and numerous guns, he had left part of his infantry in Lublin and a siege was out of the question. Harried constantly by Czarniecki and abandoned by Koniecpolski, Charles faced encirclement, as John Casimir’s army swelled to 30,000 by March. With Sapieha’s Lithuanians on the eastern bank of the San, and Czarniecki rapidly approaching from the south, Charles retreated north but was trapped in the confluence of the Vistula and the San and facing disaster with 5,500 men against over 20,000.
As the Poles waited for their artillery and infantry, Charles escaped with characteristic bravado before the trap snapped shut. Forcing his way over the San under cover of darkness on 5–6 April he broke through the Lithuanians, who had no infantry or guns. It cost him most of his artillery and much of his baggage, together with a relief force of some 4,500 cavalry and dragoons which had set off from Warsaw under Margrave Frederick of Baden, turning back when Frederick heard that Czarniecki and Lubomirski were approaching. The slower-moving Swedish force was caught at Warka on 7 April and destroyed. Frederick had performed his function, however: by drawing Czarniecki away from Sandomierz, he had prevented him reinforcing Sapieha’s Lithuanians as had been intended, which would have seriously reduced Charles’s chances of escape.
The tide had turned with a vengeance. It was clear that the forces at Sweden’s disposal were insufficient to force a quick end to the war. The dash to the south had meant that Charles had to abandon any hopes of a quick capture of Danzig, while the Poles had cleared the Vistula between Cracow and Warsaw. John Casimir arrived at the capital in June with 28,500 regulars and 18–20,000 from the noble levy. On 29 June a force of peasant infantry stormed the city. In these circumstances, Charles could only turn to diplomacy. At Marienburg on 25 June 1656, Frederick William signed a military alliance with Sweden, in return for the grant of hereditary sovereignty over Wielkopolska, although he was to remain a Swedish vassal in Ducal Prussia.
The result was the battle of Warsaw (28–30 July 1656), in which Charles demonstrated just how much the Swedes had learned from the Poles: while the allied infantry played its part, it was the cavalry on which victory depended. It was the Poles who, despite the composition of their army, tried to fight a western-style battle: the forces at John Casimir’s disposal consisted of 24–25,000 regulars, 2,000 Tatars and 10–13,000 from the noble levy – about 40,000 men, of which a mere 4,500 were infantry. After a disagreement with Czarniecki, who argued that the Poles should avoid open battle in the light of Swedish firepower, John Casimir ferried his army across the Vistula, intending to march up the right bank to attack the Swedish camp; Czarniecki was sent with 2,000 horse up the left bank to prevent a Swedish attack on that side of the river.
Charles now seized the initiative. The allied army was a mere 18,000 strong, but its composition is striking: it contained sixty cavalry squadrons (12,500 men) and a mere fifteen infantry brigades (5,500 men), only 1,000 more than the Poles. With this mobile force, Charles marched down the right bank of the Vistula on 28 July to mount a frontal assault on the Poles, most of whose infantry was dug in across a narrow corridor of open land beside the river. The next day, unable to dislodge them, Charles carried out a bold and highly risky manoeuvre which was only possible with a largely cavalry army. Wheeling left through the Bialolecki forest, with his infantry shielded by the cavalry, he moved his entire force onto the narrow plain which opened up on the Polish right. By the time the Poles launched Polubinski’s hussars at the allies they had consolidated their position.
The charge was launched not against the allied infantry in the centre, but against the reiter units that flanked it. Although they suffered from infantry flanking fire, the hussars smashed into the reiters, with the brunt of the impact absorbed by the Uppland and Småland regiments. The hussars performed their primary task, breaking through the first line and penetrating into the second, where they were brought to a halt and forced back. The failure of the attack was due to the deployment of the allied cavalry in three lines, which gave the necessary depth to the defence, and by their numbers. For the Poles, the main problem was that the initial attack was not followed up; John Casimir simply had too few hussars, the most expensive formation in the army. A maximum of 800 took part in Polubinski’s charge; it was not enough, and the pancema cavalry in reserve did not press home the attack. The allies held their ground; deciding that the battle was lost, John Casimir began to withdraw across the single bridge over the Vistula. The next day the allies rolled forward across the open plain; as the Polish-Lithuanian cavalry escaped north and south along the Vistula, John Casimir abandoned his capital for the second time in twelve months. The Poles had been beaten at their own game; the ghost of Kircholm had finally been laid to rest.
Warsaw was a famous victory, but the Swedes derived little benefit. The allies set off in pursuit, occupying Radom on 10 August, but Frederick William had no intention of supporting further Swedish gains. With Brandenburg garrisons having replaced the Swedes in Wielkopolska, the elector refused further military cooperation. Since the Brandenburg contingent of 8,500 had constituted nearly half the allied army at Warsaw, Charles’s own forces were inadequate for any sustained campaign. Withdrawing his isolated garrisons from the Sandomierz palatinate, he strengthened the Cracow garrison and withdrew north to Royal Prussia, where Danzig was still resistin