During 1641, the Swedish army narrowly escaped the pursuit by Imperials and Bavarians after its failed attack on the
Imperial Diet in
Regensburg in January. Its commander
Johan Banér lost several thousand men at the battles of
Neunburg and
Preßnitz until his untimely death at
Halberstadt in May. With the help of their French and
Guelph allies, the remnant of the Swedes repelled the Imperials at
Wolfenbüttel but only the arrival of
Lennart Torstensson in November with fresh recruits and the outstanding pay saved them from mutiny. The Emperor's peace with the Guelphs in the Treaty of Goslar removed the strategic link between the Swedes and the French army under
Jean-Baptiste Budes de Guébriant, forcing the French to turn west where they defeated an Imperial army under
Guillaume de Lamboy at
Kempen in early 1642. Because of Kempen, the Westphalian army under
Melchior von Hatzfeld and the Bavarians under
Franz von Mercy split up from the main Imperial force to contain Guébriant's advance. Imperials and Swedes moved to the east where the Swedes pitched winter quarters in
Brandenburg, which had declared neutrality in 1641. Brandenburger denial of military access to the Imperials prevented them from assaulting the Swedes in February 1642. The Imperial commander Archduke Leopold Wilhelm was compelled to retreat from
Genthin in the
Bishopric of Magdeburg to move into winter quarters in late February. While the Imperials were still obtaining quarters in April, the Swedes already started their campaign. The new Swedish commander Torstensson planned an offensive in 1642 to strike into the
Habsburg lands. While a mobile force under
Hans Christoff von Königsmarck raided westwards towards
Quedlinburg as a distraction, Torstensson moved east to
Lusatia from where he invaded
Silesia. He took
Głogów, one of its strongest fortresses, by storm on 4 May. The Imperial commander in Silesia, Franz Albrecht of Saxe-Lauenburg, collected a small army of 7,500 men and called
Archduke Leopold Wilhelm of Austria for aid. Before being reinforced by a detachment from the main Imperial Army under
Ottavio Piccolomini, Franz Albrecht tried to relieve the siege of
Schweidnitz. Tricked into attacking a much larger Swedish force on 31 May, his troops were overwhelmed and he was mortally wounded. Piccolomini withdrew to
Brno to join with the Archduke, while on 14 June Torstensson captured
Olomouc in
Moravia after a short siege. After collecting superior forces, the Imperials forced the outnumbered Swedes back into Silesia, pursued by the Archduke. Leaving a blockading corps at Olomouc, on 25 July his
vanguard under
Raimondo Montecuccoli defeated a Swedish detachment at
Troppau which was screening the siege of
Brieg, forcing Torstensson to abandon it and retreat across the
Oder river. The Archduke laid siege to Głogów on 10 August but abandoned it on 12 September when Torstensson offered him battle in front of the fortress. The Swedish army was now large enough to put the Imperials under pressure and they pulled back to the Bohemian border where they entrenched themselves and used their light cavalry to harass the Swedish supply lines. Withdrawing into Saxony in October, Torstensson laid siege to
Leipzig, the second-largest city in Saxony and an important stronghold for
John George I, Elector of Saxony, an Imperial ally. ==Battle==