The Treaty of Stettin (Swedish: Traktaten or Fördraget i Stettin) or Alliance of Stettin (German: Stettiner Allianz) was the legal framework for the occupation of the Duchy of Pomerania by the Swedish Empire during the Thirty Years' War. Concluded on 25 August (O.S.) or 4 September 1630 (N.S.), it was predated to 10 July (O.S.) or 20 July 1630 (N.S.), the date of the Swedish Landing. Sweden assumed military control, and used the Pomeranian bridgehead for campaigns into Central and Southern Germany. After the death of the last Pomeranian duke in 1637, forces of the Holy Roman Empire invaded Pomerania to enforce Brandenburg's claims on succession, but they were defeated by Sweden in the ensuing battles. Some of the Pomeranian nobility had changed sides and supported Brandenburg. By the end of the war, the treaty was superseded by the Peace of Westphalia (1648) and the subsequent Treaty of Stettin (1653), when Pomerania was partitioned into a western, Swedish part (Western Pomerania, thenceforth Swedish Pomerania), and an eastern, Brandenburgian part (Farther Pomerania, thenceforth the Brandenburg-Prussian Province of Pomerania).
Background
Following the Capitulation of Franzburg in 1627, the Duchy of Pomerania was occupied by forces of Ferdinand II, Holy Roman Emperor, under command of Albrecht von Wallenstein. The Swedish intervention in the Thirty Years' War began with the active military support of Stralsund, a Pomeranian Hanseatic port which since the Battle of Stralsund successfully resisted imperial occupation with Danish and Swedish support. Sweden and Stralsund concluded an alliance scheduled for twenty years. The Danish campaigns in Pomerania and other parts of the Holy Roman Empire ended with the Battle of Wolgast in 1628 and the subsequent Treaty of Lübeck in 1629. Except for Stralsund, all of Northern Germany was occupied by forces of the emperor and the Catholic League. In 1629, the emperor initiated the Re-Catholization of these Protestant territories by issuing the Edict of Restitution.
The Truce of Altmark ended the Polish–Swedish War (1626–1629) in September 1629, releasing the military capacities needed for an invasion of the Holy Roman Empire. Plans of Gustavus Adolphus of Sweden for such an intervention were approved of by a Riksdag commission already in the winter of 1627/28, approval by the Riksråd followed in January 1629.
On 26 June (O.S.) or 6 July (N.S.) 1630, Gustavus Adolphus of Sweden with a fleet of 27 ships arrived at the island of Usedom and made landfall near Peenemünde with 13,000 troops (10,000 infantry and 3,000 cavalry on thirteen transport ships). The core of the invasion force consisted of trained peasants, recruited to the Swedish army following Gustavus Adolphus' military reforms of 1623. The western flank of the Swedish invasion force was cleared from Stralsund, which served as the basis for Swedish forces clearing Rügen and the adjacent mainland from 29 March until June 1630. The officially stated Swedish motives were:
The Swedish landing force faced Albrecht von Wallenstein's imperial occupation forces in Pomerania, commanded by Torquato Conti. Large parts of the imperial army were pinned down in Italy and unable to react. Wallenstein, who two years before had expelled the Danish landing forces at the same place was about to be dismissed. On 9 July, Swedish forces took Stettin (now Szczecin), but throughout 1630 were content with establishing themselves in the Oder estuary.
The treaty and amendments
The first draft of a Swedish-Pomeranian alliance, which the Pomeranian ducal councillors had worked out since 20 July 1630 (N.S.), was rejected by Gustavus Adolphus of Sweden. A second draft was returned to the council together with a list of modifications Sweden insisted on. On 22 August (N.S.), actual Swedish-Pomeranian negotiations started, which Gustavus Adolphus on 1 September (N.S.) joined in person. The final negotiations lasted from 2–4 September (N.S.).
The actual agreement was made on 25 August (O.S.) or 4 September (N.S.), but pre-dated to 10 July (O.S.) or 20 July 1630 (N.S.). The alliance was to be "eternal". The treaty also included the alliance with Stralsund of 1628, which was concluded when the town resisted the Capitulation of Franzburg and was thus besieged by Albrecht von Wallenstein's army.
Subsequent treaties were the "Pomeranian Defense Constitution" of 30 August 1630 (O.S.), and the "Quartering Order" of 1631. The Swedish king and the high-ranking officers were given absolute control over the duchy's military affairs, while the political and ecclesial power remained with the dukes, nobles, and towns. The duchy's foreign affairs were to be within the responsibility of the Swedish crown. The amending treaties were necessary because the Pomeranian nobility had insisted on having the shift in military control of the duchy to Sweden separate from the Swedish-Pomeranian alliance.
The Pomeranian contributions detailed in the treaties amounted to an annual 100,000 Talers. Furthermore, Pomerania was obliged to supply four Swedish garrisons.
The alliance
Implementation in Pomerania
When Bogislaw XIV, Duke of Pomerania had concluded the alliance, he immediately wrote a letter to Ferdinand II, Holy Roman Emperor, reading
"This union is not directed against the majesty of the Emperor or the Empire, but is rather designed to maintain the constitution of the Empire in its ancient state of liberty and tranquillity, and to protect the religious and secular settlements against the ravagers and disturbers of the public peace, and thereby not only to leave intact the relationship which binds us, Bogislaw XIV [...] to His Imperial Roman Majesty [...] but also to preserve our lawful duty and obligations to the same."
Bogislaw XIV further blamed the "barbarities and cruelties of the Imperial soldiers" for leaving him no choice. Yet, Ferdinand II did not forgive Bogislaw XIV, and instead the imperial occupation forces in Pomerania were instructed to act even more harshly. As a consequence, raids were conducted frequently, buildings and villages were burned, and the population was tormented. The imperial atrocities became one argument for the Pomeranian population to support Sweden. Another argument was that in contrast to Pomerania, there was no serfdom in Sweden, and thus the Pomeranian peasants held a very positive view of the Swedish soldiers, who were in fact peasants in arms.
With the aforementioned treaties, Sweden included the Pomeranian duchy in her military contributions' system, enabling her to triple the size of her forces there within a short period. In 1630, Carl Banér was appointed Swedish legate in Stettin, succeeded in 1631 by Steno or Sten Svantesson Bielke, who in 1630 was the Swedish commander in Stralsund.
From the Oder estuary bridgehead, the Swedish forces subsequently cleared the Duchy of Pomerania of imperial forces in 1631. The Pomeranian towns of Gartz (Oder) and Greifenhagen (now Gryfino), both south of Stettin, were attacked on 4 and 5 January 1631. The imperial occupation forces had established a defense in both towns since 4 and 7 June 1630. With these taken, Sweden was able to advance further south into Brandenburg, and west into Western Pomerania and Mecklenburg. The last imperial stronghold in Pomerania was Greifswald, which was besieged by Sweden since 12 June 1631. When imperial commander Perusi was shot during a ride, the imperial garrison surrendered on 16 June. Gustavus Adolphus of Sweden even returned from Brandenburg to supervise the siege, and upon his arrival received the university's homage for the liberation.
Support for Sweden among the peasants did not fade even when they were mobilized and recruited for military construction works. A different situation emerged in the towns, where burghers were often in conflict with the garrison. While the Swedish king issued several decrees ruling and restricting the interaction of soldiers and burghers, this did not prevent "turmoils against the undisciplined soldatesca" already in 1632. The larger towns often refused to fulfill the demands of the Swedish military.
Bridgehead for the Swedish intervention in the Holy Roman Empire
When Gustavus Adolphus landed in Pomerania, the German Protestant nobility met his intervention with distrust. In April 1631, at a convention in Leipzig, they decided to set up a third front on their own, and except for Magdeburg, who had allied with Sweden already on 1 August 1630, did not side with Sweden. In Swedish strategy, Magdeburg was to be the spark inflaming a "universal rebellion in Germany" – yet initially this strategy failed.
In early 1631, Swedish forces advanced into Brandenburgian territory. On 23 January 1631, Sweden concluded an alliance with France in Brandenburgian Bärwalde (now Mieszkowice) near Greiffenhagen. Brandenburgian Frankfurt (Oder) and Landsberg (Warthe) (now Gorzow) were taken on 15 and 23 April, respectively. Subsequently, Brandenburg was forced into treaties with Sweden on 14 May, 20 June and 10 September 1631. While these obliged George William, Elector of Brandenburg to hand over control of the Brandenburgian military to Sweden, he refused to enter an alliance.
Sweden was not able to support Magdeburg, and in the summer of 1631, the town was taken and looted by Johann Tserclaes, Count of Tilly's forces. When a fire destroyed what was left of the town, and 20,000 inhabitants were burned, the Protestants' scepsis turned into support for the Swedish king. When Tilly attacked the Electorate of Saxony, the Saxon elector joined his forces with the Swedish army, and the combined forces decisively defeated Tilly in the Battle of Breitenfeld (1631). This defeat of the combined imperial and Catholic League forces allowed Sweden to pursue deep into Central and Southern Germany.
After Gustavus Adolphus' death
Gustavus Adolphus was killed in the Battle of Lützen on 6 November 1632. George William, Elector of Brandenburg, joined the obsequies in Stettin on 31 May, and proposed joining the Alliance of Stettin if he would in turn participate in the Pomeranian succession. Bogislaw XIV, Duke of Pomerania, the last living member of the House of Pomerania, had suffered a stroke already in April 1631. Sweden neither approved nor rejected the Brandenburgian offer. On 19 November 1634, a "regiment constitution" reformed the administration of the duchy of Pomerania. The two governments in Wolgast and Stettin resulting from the partition of 1569 had already been merged on 18 March. The new constitution reformed this government to consist of a proconsul, a president, and seven members.
After Sweden had to acknowledge her first serious defeat in the Battle of Nördlingen (1634), Ferdinand II, Holy Roman Emperor and several Protestant states concluded the Peace of Prague in May 1635. Calvinist Brandenburg was reluctant to sign, since besides the announced annulment of the Edict of Restitution, toleration of Calvinism was not mentioned. To get Brandenburg to sign up, Sweden and Ferdinand promised her the succession in the Duchy of Pomerania in return.
Another consequence of the lost Battle of Nördlingen was that large parts of the Swedish army, including thousands of injured, retreated to Pomerania, followed by imperial forces who entered the duchy in 1636. The riksråd considered to abandon all of Pomerania except for Stralsund. Both the atrocities committed by the Swedish soldiers and the contributions paid by Pomerania for the military peaked during the following years. Short of supplies, the Swedish as well as the imperial mercenaries forced their means of subsistence from the local population. In 1637, a capitulation was issued that mentions "irruption" and "insolentia" by the military, and ruled out more drastic consequences for irregular behaviour of the soldiers.
On 24 February 1637, the Pomeranian councillors decided that the Pomeranian constitution of 1634 should remain in effect in case of the duke's death, which was approved of by Sweden and rejected by Brandenburg.
After Bogislaw XIV's death – Confrontation with Brandenburg
On 10 March 1637, Bogislaw XIV died without issue. Swedish legate Sten Svantesson Bielke on 11 March advised the Pomeranian council to nevertheless adhere to the Alliance of Stettin, and to reject any Brandenburgian interference. George William, Elector of Brandenburg, in turn mailed Christina of Sweden on 14 March to respect his succession in the Pomeranian duchy based on the treaties of Pyritz (1493) and Grimnitz (1529), on which the alliance did not have any impact. Similar letters addressed Bielke, and Swedish field-marshal Carl Gustaf Wrangel. The same day, a courier arrived in Stettin with the elector's seizure patent, who at once was incarcerated by Bielke and threatened with death by hanging. The next day, the Brandenburgian elector admonished the Pomeranian nobility to behave as his subjects.