Banér joined the
Swedish Army in 1615, and distinguished himself during the Swedish
Siege of Pskov. He served with distinction in wars against
Russia and
Poland, and had reached the rank of
colonel by the age of 25. In 1630, Gustavus Adolphus landed in
Germany to assist German Protestant forces in the Thirty Years War, and, as one of the king's chief subordinates, Banér served in the campaign of north Germany, including leading the right wing of
Swedish cavalry at the first
Battle of Breitenfeld. He was present at the taking of
Augsburg and
Munich, and rendered conspicuous service at the
Lech and at
Donauwörth. At the unsuccessful assault on
Albrecht von Wallenstein's camp at the
Alte Veste, Banér received a wound, and soon afterwards, when Gustavus marched towards
Lützen, was left in command in the west, where he opposed the imperial general
Johann von Aldringen. Two years later, as Swedish field marshal, Banér, with 16,000 men, entered
Bohemia and, combining with the Saxon army, marched on
Prague. However, the complete defeat of
Bernard of Saxe-Weimar in the first
Battle of Nördlingen stopped his victorious advance. After this event, the
Peace of Prague placed the Swedish army in a very precarious position, but the victories won by the united forces of Banér and
Alexander Leslie at
Wittstock (4 October 1636), restored the paramount influence of Sweden in central Germany. Banér, in his report to
Queen Christina on the battle of Wittstock, stated the following: "[My soldiers] would have fallen into total disorder if Field-Marshal Leslie with the five brigades of foot which he had with him during the battle had not assisted us just in time and manfully attacked and turned 4 brigades of the enemy’s infantry away from us so that we could finally gain our breath". However, the three combined armies were considerably inferior in force to those they had defeated, and in 1637 Banér was unable to make headway against the enemy. Rescuing with great difficulty the beleaguered garrison of
Torgau, he retreated beyond the
Oder into
Pomerania. In 1639, however, he again overran northern
Germany, defeated the
Saxons at
Chemnitz and invaded
Bohemia itself. The winter of 1640–1641 Banér spent in the west. His last achievement was an audacious
coup de main on the
Danube. Breaking camp in mid-winter (a very rare event in the 17th century), he united with the
French under the
Comte de Guébriant and surprised
Regensburg, where the
Diet was sitting. Only the break-up of the ice prevented the capture of the place. Banér thereupon had to retreat to
Halberstadt. Here, on 10 May 1641, he died, possibly due to advanced
liver cirrhosis caused by his excessive alcohol consumption, after designating
Lennart Torstenson as his successor. He was much beloved by his men, who bore his body with them on the field of
Wolfenbüttel. On the other hand, the enemies of Sweden rejoiced and a parody requiem hoping that he was burning in hell was even composed in
Bohemia, which had been badly pillaged by Banér. where his armour is also on display. ==Assessment==