The bisthum of Münster had been a German country governed by the Catholic church for many centuries.
Since the Sacco di Roma however, pilgrims returning from Rome with the bad news had spread discontent in Germany. The break came in 1475: When king Heinrich VIII secularized and annexed the bistums of Augsburg and Trient for his lands, the HRE fell into a kind of Civil War. All the princes tried to annex the clerical lands, which led to lots of confusion and little wars for said lands, which are subsumed as the Twenty-Year War.
In the same year, in the bisthums of Würzburg and Münster, millenialist sects took the power, declared the Gottesfreistaat (God's republic - another kind of theocracy). The latter ones even managed to extend their lands during the chaos of the war, deposing some small princes of NW Germany. Both states ignored the HRE and its emperor for their concerns.
When the war was over, however, the German princes remembered the Gottesfreistaaten again. During the reforms of the HRE (1500-08), the Gottesfreistaaten of Münster and Würzburg were put into Reichsacht (meaning: everyone was officially allowed kill their people and take their lands).
While Würzburg wasn't that lucky (in 1545, burgrave Johann II von Hohenzollern of Ansbach and Bayreuth defeated the Gottesfreistaat and annexed it, thus forming the new duchy of Franconia), Münster would continue for longer and even could expand its territory: 1560-66, the Netherlands made war against them, but were defeated. In 1581/82, Münster attacked the little country of Oldenburg and conquered it. But this was the last straw. The Netherlands and Nassau felt seriously threatened, asked the Triple Monarchy of England-Castille-Portugal for support. In the Netherlands this didn't work out because their king died in an unfortunate incident, but Nassau received help (in the form of French musketeers) and defeated Münster, annexing the territories of Tecklenburg, Ravensberg, Paderborn. The religious dissenters who didn't want to reconvert fled, some of them even to Atlantis. Nassau completely defeated Münster with French help in 1676-79, annexing it in the end. Many Münsteraner fled, again, to Atlantis. Denmark-Braunschweig was angered somewhat because France had promised them Münster earlier.
Note that Münster was named after its capital Münster.
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