Why was Luxembourg divided between Belgium and the grand duchy in 1839?

The division of Luxembourg in 1839 was a result of the Belgian Revolution of 1830, during which Luxembourgish citizens supported the Belgian uprising against the rule of William I, King of the Netherlands.12

Following the revolution, the Belgian government declared the grand duchy part of Belgium, while William I maintained his claim to the territory. To resolve the conflict, the great powers—France, Britain, Prussia, Russia, and Austria—intervened. In 1831, they proposed that the French-speaking portion of the duchy be assigned to Belgium, while the Luxembourgish-speaking portion remain under the possession of William I as part of the German Confederation.12

Although William I initially rejected this settlement, he eventually acceded to the arrangement in 1839. Consequently, the western half of the territory became a Belgian province named Luxembourg, while the eastern half remained the Grand Duchy of Luxembourg.123