Hessian War The Hessian War ( ) , in its wider sense sometimes also called the Hessian Wars ( " Hessenkriege " ) , was a drawn out conflict that took place over many years , sometimes pursued through diplomatic means , sometimes by military force , between branches of the princely House of Hesse , particularly between the Landgraviate of Hesse - Cassel and the Landgraviate of Hesse - Darmstadt . It was triggered by a division of inheritance following the death of the last landgrave of all Hesse , Philip I in 1567 . The real conflict , which lasted almost 80 years and spanned three generations , escalated in the 1620s , when the line of Hesse - Marburg died out , and peaked after 1645 in the Hessian War proper . This open warfare began with the Siege of Marburg in 1645 and ended inApril 1648 ( but before the Treaty of Westphalia which was concluded later that year and ended the Thirty Years ' War ) with victory going to Hesse - Cassel . In the aftermath , Upper Hesse was divided and parts of its territory went to the now stronger Hesse - Cassel . At a European level the Hessian War must be viewed in the larger context of the Thirty Years ' War , in which the reformed Hesse - Cassel sided with the Protestant Swedish party , whilst Hesse - Darmstadt , despite its Lutheran confession joined the Catholic - Imperial alliance . In the course of the war , Hessian mercenaries fought both in the main Hessian lands as well as in Westphalia ( Prince - Bishopric of Münster and Paderborn ) , in Upper Guelders , on the Lower Rhine ( Electorate of Cologne ) , in the Duchy of Brunswick and other places . This conflict should not be confused with the campaign by Landgrave Philip I of Hesse , supported by Prince - Elector John of Saxony against the two Frankish prince - bishoprics of Würzburg and Bamberg in 1528 , which is also referred to as the " Hessian War " . Course of the war . Cause and opening phase . The cause of the conflict was the division of inheritance following the death of Phillip the Magnanimous in 1567 . According to an old house law in the House of Hesse , he had mandated in his will a division of the landgraviate amongst his four sons , whereby the inheritance of Hessian territory was as follows : When the Rheinfels line died out in 1583 Hessen - Rheinfels was divided amongst the three remaining brothers of Philip II . The dispute over the Marburg inheritance and the Thirty Years ' War . Marburg Inheritance Dispute ( from 1604 ) . In 1604 , Landgrave Louis IV of Hesse - Marburg died without issue at his castle in Marburg . His will envisaged that Hesse - Marburg would be divided equally between the sons of his late brothers , William in Cassel and George in Darmstadt , on the condition , that the whole of Hesse - Marburg continued to follow the Lutheran confession . There was initially a dispute over whether each of the two remaining lines of the family should receive exactly half the territory or whether it should be split according to the number of nephews in each case . Darmstadt would have benefited from the latter interpretation , because George of Hesse - Darmstadt had produced more sons ( Louis , Philip ( III ) and Frederick ) than William of Hesse - Cassel with just one heir , Maurice . Following an action for annulment by Hesse - Darmstadt , the matter was decided in favour of Hesse - Cassel by the Aulic Council ( " Reichshofrat " ) , and Hesse - Marburg was divided in half . In 1605 , the dispute over the Marburg inheritance flared up again after Landgrave Maurice of Hesse - Cassel , whose beliefs since his accession in 1592 increasingly moved towars the Calvinistic confession of his wife , Juliana of Nassau - Dillenburg , enacted several Calvinist - oriented laws in his domain and in the same year , converted to Calvinism himself . In the wake of this , many Lutheran priests moved to Hesse - Darmstadt and the Lutheran theologians of the University of Marburg went to the " gymnasium illustre " in Gießen , which , in 1607 also achieved the status of a university . Because , Maurice , by his conversion to Calvinism had ended the Lutheran unity of Hesse - Marburg , he fell foul of the will of his uncle , thus forfeiting his claim to his portion of Hesse - Marburg in the view of Hesse - Darmstadt . Darmstadt was at this point in time neither politically nor militarily strong enough to be able to pursue its claim to the whole of Hesse - Marburg . The rise of Hesse - Darmstadt to the " Hauptakkord " ( 1618 – 1627 ) . During the Thirty Years ' War , or more precisely War over Electoral Palatine , Louis V of Hesse - Darmstadt initially remained neutral but , despite the fact that his state embraced the Lutheran confession , he increasingly sided with the Roman Catholic emperor , whilst the Calvinist Hesse - Cassel fought with the Protestant Union . After the Protestant Duke Christian of Brunswick - Wolfenbüttel had invaded Upper Hesse in 1621 , Louis V openly allied himself with the emperor in the hope of receiving military support . This gamble l paid off in the medium term : in 1621 the imperial Field Marshal Ambrosio Spinola occupied the Wetterau . In reply , the commander of the Protestant army , Ernst von Mansfeld , counter - attacked the Darmstadt upper county on orders of Prince - Elector Frederick of the Palatinate . In doing so he succeeded in taking Louis V of Hesse - Darmstadt and his son , John , prisoner . In exchange for the release of the hostages he was given the fortress of Rüsselsheim . During his withdrawal from Russelsheim , however , Mansfeld was defeated on 10 June 1622 in the battle on the Lorsch Heath by imperial general , Tilly . A few weeks earlier , on 27 April 1622 in the Battle of Mingolsheim , Mansfeld had triumphed against Tilly , but achieved no great advantage from his victory . In the meantime , Tilly had grown in strength following his victory at the Battle of Wimpfen on 6 May 1622 . Mansfeld defeated Tilly on 20 June 1622 , as well as Duke Christian of Brunswick - Wolfenbüttel in the Hessian region at Höchst am Main in the Battle of Höchst , as a result of which the Protestant side was significantly weakened . Tilly advanced again against Hesse - Cassel and occupied all of Lower Hesse as far as the city of Cassel . As a result , he enforced the Aulic Council ' s judgement of 11 April 1623 , that the entire heritage of Hesse - Marburg ( including all tax revenue from it , retroactively ) should go to the Darmstadt line . Tilly also occupied several Lower Hessian offices as a security . Even the former county of Katzenelenbogen was seized from Darmstadt . Landgrave Louis V died during the campaign . His son , George II , took over the reins of power in Darmstadt and continued the fight against Cassel . Because of military defeats and abject government by Landgrave Maurice of Hesse - Cassel , the Lower Hess estates openly rebelled against him and forced his abdication in 1627 . The House of Cassel also lost Hesse - Rotenburg ( the so - called " Rotenburger Quart " ) thanks to Maurice ' s division of his inheritance . Thus weakened , Maurice ' s son and heir , William V , was forced to accept the judgment of the Aulic Council in 1623 and cede the disputed territories . On 24 September 1627 a settlement was reached , the so - called " Hauptakkord " . The whole of Upper Hesse , the Lower County of Katzenelnbogen and the Barony of Schmalkalden , a Hessian exclave in Thuringia , went to Hesse - Darmstadt . In addition , Hesse - Cassel and Hesse - Darmstadt were granted the same level of precedence in the German Empire . In return , Hesse - Cassel was given back the territories in Lower Hesse that had been held as a security . Following the Edict of Restitution of 1629 Hesse - Cassel was also given the Imperial Abbey of Hersfeld , which had been under Lower Hessian rule since 1604 . The rise of Hesse - Cassel in the Swedish War ( 1630 – 1634 ) . After the total defeat of the House of Hesse - Cassel had been averted by the " Hauptakkord " , in 1627 William V began secretly waiver , to build a new mercenary army , under the cover of his apparent renunciation . The turning point for Hesse - Cassel in the Thirty Years ' War came in October 1630 when William V became the first German Protestant prince to ally himself with King Gustavus II Adolphus of Sweden ( also a great - grandson of Philip I and thus a cousin of William V ) . After the alliance was formally sealed on 22 August 1631 in the Treaty of Werben ( in the wake of the Battle of Werben ) , Hesse - Cassel placed its army in the service of the Swedish king . In return , Gustavus Adolphus held out the prospect to Cassel that they could expand their territory by conquest . With the political and military support of the Protestantischen alliance under the leadership of the Swedish king and thanks to the skillful leadership of William V , who himself went to war as a general , in the period that followed the Lower Hessian troops achieved considerable military success . As a start , they succeeded in driving the imperial occupiers out of Hesse - Cassel . On 24 August 1631 , Hersfeld was conquered and , on 9 September 1631 , the town of Fritzlar that belonged to the Electorate of Mainz . The imperial troops were further weakened by their defeat in the Battle of Breitenfeld and came under pressure . By mounting diversionary attacks on Mainz positions in the Taunus , Hesse - Cassel supported the Swedish advance on Erfurt , Würzburg and Hanau to Frankfurt and Mainz . The hopes of Lower Hesse to recover their lost territories in Upper Hesse , as a reward for their support of Sweden , were not , however , fulfilled . After George II of Hesse - Darmstadt had concluded negotiations with the Swedish king , he succeeded in gaining recognition of the neutrality of Hesse - Darmstadt at the Treaty of Höchst on 29 November 1631 , in exchange for giving up the fortress of Rüsselsheim , so that Darmstadt was able to keep its territories in Upper Hesse . Instead , on 28 February 1632 , Gustavus Adolphus granted Hesse - Cassel several other areas outside of Hesse that the Lower Hessian troops had conquered earlier on Swedish orders ( including the Fulda Abbey , the Bishopric of Paderborn and Corvey Abbey ) or intended to capture ( the Bishopric of Münster , later substituted by the Swedish Chancellor Oxenstierna for parts of the Duchy of Westphalia and Vest Recklinghausen ) . Advance by the Emperor on Hesse - Cassel from 1634 . After the Battle of Lützen in November 1632 , in which the Swedish - Protestant side suffered great losses and King Gustavus Adolphus was killed , the fortunes of war turned against the Protestants , including Hesse - Cassel . Following their defeat in the Battle of Nördlingen in September 1634 the Protestant Alliance crumbled . The Calvinist Hesse - Cassel could not comply with the Treaty of Prague of 1635 as a result of excessive demands from Darmstadt , which insisted on the annexation of the whole of Hesse - Cassel . Later it fought once again on the Swedish and French side against the Emperor and the Imperial Prince s because of the uncompromising politics of the imperial court . On the opposing side , Hesse - Darmstadt had given up its neutrality and fought openly again for the Emperor . Both sides scored successes . For example , Darmstadt won the County of Isenburg - Büdingen and the Electoral Palatine Amt of Caub . On 13 June 1636 , Cassel ended a nine - month blockade of the fortress of Hanau with a victory over the imperial army commander , Lamboy . But neither side won a decisive victory . In response to his victory over the imperial troops in Hanau and his alliance with France , William V of Hesse - Cassel was outlawed on 19 August 1636 by the electors at Regensburg . His adversary from Darmstadt was appointed administrator over all of Hesse . However , because of the military stalemate , the ban was initially ineffective . Because even after more than two decades , no end to the confrontation was in sight and the whole of Hesse was suffering badly from the consequences of the war , more so than almost any other region in Germany , in February 1637 the " Landstände " , or knightly estates , from all parts of Hesse organized a " Landtag " to seek a mediation between their lords . But this arbitration parliament was not successful because , in parallel , the newly elected Emperor Ferdinand III , also King of Croatia , had already sent several regiments of Croatian troops to Lower Hesse to the enforce the ban against William V . During their campaign the Croats devastated large parts of Lower Hesse and also threatened to take Cassel . In this situation , William V fled with his family and a large part of his army to East Frisia , where he was granted refuge by Ulrich II of East Frisia following mediation by the states - general . There , in the encampment at Leer , he died from disease on 21 September 1637 . Resurgence of Hesse - Cassel in the Swedish - Prussian War ( from 1637 ) . Because William ' s son , William VI was only eight years old at the time of his father ' s death , William V appointed his wife Amalie Elisabeth in his will as a guardian for his under - age heir and thus as regent of Hesse - Cassel . In a coup , she had the Emperor and Darmstadt pay homage to her infant son who was not subject to the ban . Elisabeth Amalie proved a skilful tactician , who succeeded in spite of her extremely difficult starting position in consolidating the position of Hesse - Cassel . First she agreed an apparent truce with the Emperor and so kept Cassel from being conquered by the Imperial Croatian forces . Then she built a powerful army again based on the cadre of troops that her husband had taken to Frisia . Furthermore , in 1639 at Dorsten , she concluded an alliance with France , represented by Cardinal Richelieu , and Sweden ; and , later , another alliance with Duke Bernard of Saxe - Weimar . In 1649 , with her new allies behind her , Amalie Elisabeth ' s troops moved in greater strength against the Electorate of Cologne in order to defend the already conquered electoral territories ( promised by Sweden in return for giving up Upper Hesse ) , especially in the area of Vest Recklinghausen , and to capture other domains besides . In 1641 Hesse - Cassel lost the town of Dorsten in Vest Recklinghausen , which they had seized in 1633 , to troops of the Imperial Army and Electorate of Cologne after a siege lasting several weeks . This was the most important Hessian position on the right bank of Lower Rhine . But after the imperial forces partially withdrew to fight in other regions ( especially Wolfenbüttel ) , Hesse - Kassel embarked on a campaign in the electoral lands on the left bank of the Rhine . At the Battle of Kempen Heath Hesse - Cassel , with the support of French and Weimar troops , dealt the Imperial forces a heavy defeat . In the wake of this defeat , large areas in the north of the Electorate , including the Duchy of Berg , and even parts of the neutral Duchy of Jülich fell under the occupation of Hesse - Cassel . The Hessian War in its narrower sense ( 1645 – 1648 ) . Inspired by military and diplomatic successes in the Rhineland and Westphalia , Landgravine Amalia Elisabeth of Hesse - Cassel felt strong enough to take up the fight for the Marburg inheritance in 1644 . She had the " Hauptakkord " treaty of 1627 , in which Hesse - Cassel had forfeited Upper Hesse , invalidated by a subsequent legal ruling and , at the end of 1645 , sent her battle - hardened troops led by John of Geyso towards Marburg . After a short siege of Marburg and Butzbach and their surrender , the majority of Upper Hesse fell again under the rule of Kassel in early 1646 . In 1647 , an imperial army under the command of General Melander , who had recently switched sides from Cassel to Darmstadt , succeeded in recovering the town of Marburg - but not its castle . But because the town of Darmstadt and the Upper County was attacked in turn by French troops under the command of Marshal Turenne shortly thereafter , this success was short - lived . By the end of 1647 , troops from Cassel had re - occupied the majority of Lower and Upper Hesse and the Lower County of Katzenelnbogen . In early 1648 , Melander ' s troops withdrew from Marburg . The Hessian War was finally permanently settled by negotiations , that took place in parallel with the Westphalian Peace Congress mediated by Duke Ernest of Saxe - Gotha and which resulted in a unification and peace treaty that was sealed in April 1648 , ahead of the Treaty of Westphalia itself . Before the Westphalian Peace Treaty , Cassel fought one last time against the imperial side , winning the Battle of Wevelinghoven in the Rhineland , together with other Protestant troops . Darmstadt , however , was not involved in this battle . Under the Unification Treaty between Cassel and Darmstadt , Upper Hesse was permanently divided . Darmstadt had to give up a significant part of Upper Hesse to Cassel , not least Marburg and other occupied territories , including the Lower County of Katzenelnbogen and the Barony of Schmalkalden .