The siege of Cassel (March 1761) was a failed attempt by Duke Ferdinand of Brunswick to capture French-held Kassel, the capital of Hesse-Kassel. The siege lasted about four weeks, but Brunswick was forced to lift the siege after forces of the Duc de Broglie inflicted heavy casualties on his forces at the Battle of Grünberg on March 21, making continuation of the siege untenable.
In 1762, Brunswick successfully captured Cassel after the Siege of Cassel. It would remain under occupation until the end of the Seven Years War.
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Text from the Wikipedia article “Siege of Cassel”, available under CC BY-SA 4.0.