Editing Thirty Years' War (section)

===Sweden invades Germany (1630–1635)===
{{Main|Swedish intervention in the Thirty Years' War}}
[[File:Strasbourg walter gustave adolphe.JPG|left|thumb|upright=1.0|[[Gustavus Adolphus of Sweden]], known as the "Lion of the North", at the [[Battle of Breitenfeld (1631)|Battle of Breitenfeld]] in 1631]]

From 1626 to 1629, Gustavus was engaged in a [[Polish–Swedish War (1626–1629)|war with Poland–Lithuania]], ruled by his Catholic cousin [[Sigismund III Vasa|Sigismund]], who also claimed the Swedish throne and was backed by Ferdinand II. Once this conflict ended, and with only a few minor states like [[Hesse-Kassel]] still openly opposing Ferdinand, Gustavus became an obvious ally for Richelieu.{{Sfn|Maland|1980|pp=98–99}} In September 1629, the latter helped negotiate the [[Truce of Altmark]] between Sweden and Poland, freeing Gustavus to enter the war. Partly a genuine desire to support his Protestant co-religionists, like Christian he also wanted to maximise his share of the Baltic trade that provided much of Sweden's income.{{Sfn|Wedgwood|1938|pp=385–386}}

Following failed negotiations with Ferdinand II, Gustavus landed in [[Duchy of Pomerania|Pomerania]] in June 1630 with nearly 18,000 Swedish troops. Using Stralsund as a bridgehead, he marched south along the [[Oder]] towards [[Szczecin|Stettin]] and coerced [[Bogislaw XIV, Duke of Pomerania]], into agreeing an [[Treaty of Stettin (1630)|alliance]] which secured his interests in Pomerania against his rival Sigismund.{{Sfn|Norrhem|2019|pp=28–29}} As a result, the Poles turned their attention to Russia, initiating the 1632 to 1634 [[Smolensk War]].{{Sfn|Porshnev|1995|p=106}}

However, Swedish expectations of widespread German support proved unrealistic. By the end of 1630, their only new ally was the Administrator of Magdeburg, [[Christian William of Brandenburg|Christian William]] whose capital was under siege by Tilly.{{Sfn|Parker|1997|p=120}} Despite the devastation inflicted by Imperial soldiers, Saxony and Brandenburg had their own ambitions in Pomerania, which clashed with those of Gustavus; previous experience also showed inviting external powers into the Empire was easier than getting them to leave.{{Sfn|O'Connell|1968|pp=253–254}}

[[File:Sack of Magdeburg 1631.jpg|thumb|right|upright=1.0|The [[Sack of Magdeburg]] in 1631]]

Gustavus put pressure on Brandenburg by sacking Küstrin and [[Frankfurt an der Oder]], while the [[Sack of Magdeburg]] in May 1631 provided a powerful warning of the consequences of Imperial victory.{{Sfn|Parker|1997|p=128}} Once again, Richelieu used French financial power to bridge differences between the Swedes and the German princes; the 1631 [[Treaty of Bärwalde]] provided funds for the Swedes and their Protestant allies, including Saxony and Brandenburg.{{Sfn|O'Connell|1968|p=256}} These amounted to 400,000 [[Reichstaler]] per year, or one million [[French livre|livres]], plus an additional 120,000 for 1630. While less than 2% of total French income, these payments boosted that of Sweden by more than 25%, and allowed Gustavus to maintain 36,000 troops.{{Sfn|Porshnev|1995|p=38}}

Gustavus used this army to win victories at [[Battle of Breitenfeld (1631)|Breitenfeld]] in September 1631, then [[Battle of Rain|Rain]] in April 1632, where Tilly was killed.{{Sfn|Wedgwood|1938|pp=305–306}} Ferdinand turned once again to Wallenstein, who realised Gustavus was overextended and established himself at [[Fürth]], from where he could threaten his supply lines. This led to the [[Battle of the Alte Veste]] in late August, one of the largest battles of the war. An assault on the Imperial camp outside the town was bloodily repulsed, arguably the greatest blunder committed by Gustavus during his German campaign.{{Sfn|Brzezinski|2001|p=4}}

[[File:Swedish phase map.svg|left|thumb|upright=1.0|Campaigns during the Swedish phase]]

Two months later, the Swedes fought an Imperial army at [[Battle of Lützen (1632)|Lützen]]. Both sides suffered heavy casualties, while Gustavus himself was killed and some Swedish units incurred losses of over 60%.{{Sfn|Wilson|2018|p=89}} Fighting continued until dusk when Wallenstein retreated, abandoning his artillery and wounded.{{Sfn|Wilson|2018|p=89}} Despite their losses, this allowed the Swedes to claim victory, although the result continues to be disputed.{{sfn|Wilson|2018|p=99}}{{Sfn|Brzezinski|2001|p=74}}

After his death, Gustavus' policies were continued by his Chancellor [[Axel Oxenstierna]], and with French backing, Sweden and their German allies formed the [[Heilbronn League]] in April 1633. In July, their combined forces defeated an Imperial army under Bronckhorst-Gronsfeld at [[Battle of Oldendorf|Oldendorf]].{{Sfn|Wilson|2009|p=523}} Critics claimed this defeat was caused by Wallenstein's failure to support the Bavarians, while rumours spread that he was preparing to switch sides. As a result, Ferdinand II ordered his arrest in February 1634, and on 25th, he was assassinated by his own officers in Cheb.{{Sfn|Wedgwood|1938|pp=220–223}}

The loss of Wallenstein and his organisation left Ferdinand II reliant on Spain for military support. Since their main concern was to re-open the Spanish Road for their campaign against the Dutch, the focus of the war now shifted from the north to the Rhineland and Bavaria. [[Cardinal-Infante Ferdinand of Austria]], new Governor of the Spanish Netherlands, raised an army of 18,000 in Italy, which met up with an Imperial force of 15,000 at Donauwörth on 2 September 1634. Four days later, they won a decisive victory at [[Battle of Nördlingen (1634)|Nördlingen]] which destroyed Swedish power in southern Germany and led to the defection of their German allies, who now sought to make peace with the Emperor.{{Sfn|Kamen|2003|pp=385–386}}