Editing Thirty Years' War (section)

==Structural origins==
The 16th century [[Reformation]] caused [[Schmalkaldic War|open warfare]] between [[Protestants]] and [[Catholics]] within the [[Holy Roman Empire]], which ended with the 1552 [[Peace of Passau]]. The [[Peace of Augsburg]] in 1555 tried to prevent a recurrence by fixing boundaries between the two faiths, using the principle of ''[[cuius regio, eius religio]]''. Under this, states were designated as either [[Lutheran]], then the most usual form of Protestantism, or Catholic, based on the religion of their ruler. Other provisions protected substantial religious minorities in cities like [[Donauwörth]], and confirmed Lutheran ownership of property taken from the [[Catholic Church]] since 1552.{{Sfn|Parker|1997|pp=17–18}}{{efn|One major impact of the [[Reformation]] was to transfer lands and influence from the [[Catholic Church]] to secular, [[Protestant]] rulers}}

However, the settlement was undermined by the expansion of Protestantism into Catholic areas post 1555, particularly [[Calvinism]], a Protestant doctrine viewed with hostility by both Lutherans and Catholics.{{Sfn|Sutherland|1992|pp=602–603}} The Augsburg terms also gave individual rulers significantly greater autonomy, allowing larger states to pursue their own objectives. These frequently clashed with those of central authority, and on occasion superseded religion, with the Protestant states of [[Electorate of Saxony|Saxony]], [[Brandenburg-Prussia|Brandenburg]], [[Denmark–Norway]] and [[Swedish Empire|Sweden]] competing over the lucrative [[Baltic maritime trade (c. 1400–1800)|Baltic trade]].{{Sfn|Wedgwood|1938|pp=22–24}}{{efn|As below, the acquisition of territories within the Empire by [[Denmark-Norway]] and [[Swedish Empire|Sweden]] gave them an ongoing opportunity to intervene.{{Sfn|Hayden|1973|pp=1–23}}}}

Reconciling these differences was hampered by fragmented political institutions, which included 300 [[imperial estate]]s distributed across Germany, the [[Low Countries]], [[northern Italy]], and present-day France.{{Efn|Although technically there were nearly 1,800 separate imperial estates, only [[List of Imperial Diet participants (1792)|300]] were represented in the Imperial Diet or Circles. Most of the remaining 1,500 were [[imperial Knight]]s, or individual members of the lower nobility, who were excluded.{{Sfn|Wilson|2009|p=21}}}} These ranged in size and importance from the seven [[prince-elector]]s who voted for the [[Holy Roman Emperor]], down to [[prince-bishop]]rics and [[Free imperial city|imperial cities]] like [[Hamburg]].{{efn|Its official title remains ''Freie und Hansestadt Hamburg''}} Each also belonged to a regional grouping or "[[imperial circle]]", which primarily focused on defence and operated independently of the others. Above all of these was the [[Imperial Diet (Holy Roman Empire)|Imperial Diet]], which assembled infrequently, and focused on discussion, rather than legislation.{{Sfn|Wilson|2009|pp=17–22}}

Although technically elected, since 1440 the position of Emperor had been held by the [[House of Habsburg]]. The largest single landowner within the Holy Roman Empire, they ruled over eight million subjects, based in territories that included [[Archduchy of Austria|Austria]], [[Kingdom of Bohemia|Bohemia]] and [[Kingdom of Hungary|Hungary]].{{Sfn|Wedgwood|1938|p=24}} They also controlled the [[Spanish Empire]] until 1556, when [[Charles V, Holy Roman Emperor|Charles V]] divided the two empires between different branches of the family. This bond was reinforced by frequent inter-marriage, while [[Habsburg Spain|Spain]] retained territories within the Holy Roman Empire such as the [[Spanish Netherlands]], [[Duchy of Milan|Milan]] and [[Franche-Comté]]. However, although the two often collaborated, there was no such thing as a joint "Habsburg" policy.{{sfn|Frost|1994|p=102}}

This is because the two entities were very different. Spain was a global maritime superpower, stretching from Europe to the [[History of the Philippines (1565–1898)|Philippines]], and [[New Spain|the Americas]], while Austria{{efn|The [[Habsburg monarchy|lands]] ruled by the Austrian Habsburgs were often collectively known as "Austria"}} was a land-based power, focused on Germany, and securing their eastern border against the [[Ottoman Empire]].{{Sfn|Wedgwood|1938|pp=159–161}} Another key difference was the disparity in relative financial strength, with the Spanish providing large subsidies to their Austrian counterparts. The loss of these post 1640, as Spain itself struggled with the costs of a long running global war, substantially weakened the Imperial position.{{sfn|Frost|1994|pp=103-105}}

Prior to the Reformation, shared religion partially compensated for weak Imperial institutions. After 1556, rising religious and political tensions allowed states like Lutheran Saxony and Catholic [[Duchy of Bavaria|Bavaria]] to expand their own power, while further weakening Imperial authority. This internal political struggle was exacerbated by external powers with their own strategic objectives, such as Spain, the [[Dutch Republic]], or France, confronted by Habsburg lands on its borders to the [[Nord-Pas-de-Calais|north]], [[Southern France|south]], and along the [[Pyrenees]]. Since a number of foreign rulers were also imperial princes, divisions within the empire drew in players like [[Christian IV of Denmark]], who joined the war in 1625 as [[Duke of Holstein-Gottorp]].{{Sfn|Hayden|1973|pp=1–23}}