Principality of Isenburg
Timeline: The Kalmar Union
Flag Coat of Arms
Flag Coat of Arms
(and largest city)
Language German
Prince William VII
Chancellor Martin Unger
Population 432,748 
Currency HSK

The Principality of Isenburg, Isenburg, Ysenburg, is a small constitutional monarchy in central Europe. It is a member state of the Holy Roman Empire and is bordered by Hesse-Darmstadt, Fulda, Schlüchtern, Hanau, Wurzburg and Frankfurt. The population is around 432,700 and the capital is Gelnhausen.

The Head of State is Prince William VII.

The official language is German.

The currency is the Hesse Mark (HSK)


Emerging out of the Neiderlahngau in the 10th century the County of Isenburg appeared to suffer from too may heirs and an almost pathological dislike for primogeniture. It stayed a single entity until 1137, was in six parts in 1400 and eleven prior to the Fifty Years War. Many parts ended up owned, or owed their fealty to, the Archbishopric of Trier.

When Luxembourg fully absorbed Trier (see Luxembourg-Nassau) during the Fifty Years War it took all the western counties of Isenburg too, a move which might have led the dynasty into obsolescence. The fractured Eastern Isenburg territories had embraced Lutheranism, however the counts were divided in their willingness to join the Schmalkaldic League. The disposed Count Ernst of Isenburg-Isenburg, whose lands had been annexed by Trier, was briefly installed as Prince-Elector of Brandenburg in 1664 thanks to his allegiance and service to Denmark during the war, but his reactionary rule fell apart after the Luxembourgs re-entered Prague and reignited old passions.

After the war, the previously independent city of Gelnhausen was deemed too ruined to continue its independence and was handed to Isenburg-Büdingen. Although this was strenuously contested by the Counts of Hanau who argued they had a better claim over the city than the fractured Isenburgs the city would become the new capital of Isenburg. After this the Counts, then Dukes, of Isenburg-Büdingen aggressively pursued the reunification of all the Isenburg territory buying titles and land and reducing their cousins to non-sovereign sub-counts. By 1875 the final independent county had been annexed and Isenburg-Büdingen renamed itself simply as Isenburg.

Emperor William II (r. 1903-1922) was a Duke of Isenburg. His reign is often associated with the schizophrenic attitude the Empire took to the Cotton Wars which threatened economic problems for the Rhineland and Northern Italia. He was also famous for pompously arranging for his lands to be raised to a Principality. Ironically having spent so long stamping the Büdingen branch's mark on the principality the current Prince, William VII, is aging and heirless, and the Imperial Diet has been tasked with how to settle the inheritance when he dies. While it may be in local interests to allow one of the other Isenburg branches to succeed there are closer relations in foreign countries who will be put out by such a move.


Isenburg is governed by a bicameral Landstag. Elections for the lower chamber are held every four years on average while the upper chamber is made up of a hodge-podge of ancestral lords, appointed officials and token elected positions. The royal house retains various executive powers.

The current Head of State is Prince William VII. His Chancellor is Martin Unger.

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