Why did Luxembourg end its customs union with Germany after World War I?

In December 1918, the Allied powers forced Luxembourg to terminate its customs union with Germany. This decision was a consequence of the geopolitical landscape following World War I, during which Germany had violated Luxembourg’s neutrality and occupied the grand duchy until the Armistice of 1918.12

The dissolution of this economic arrangement, known as the Zollverein, had significant repercussions for Luxembourg, as it resulted in the loss of its primary supplier of coal and its most important customer for cast iron and steel. Following this forced separation, Luxembourg sought a new economic partner and eventually established the Belgium-Luxembourg Economic Union (BLEU) in 1921.12