In 1830 several francophone, Catholic and liberal groups joined forces and proclaimed the independence of Belgium, whose territory prior to that had been part of the United Kingdom of the Netherlands.

In the subsequent peace settlement in 1839, the Dutch king ceded the western half of the Grand Duchy of Luxembourg to the newly formed Belgian state.

Luxembourg however, had been a member state of the German Confederation since the latter's creation and with the annexation of its western parts lost approximately 150,000 inhabitants.

The German Confederation insisted the common market of the customs union would be compensated by the Netherlands elsewhere; the Dutch thus created the Duchy of Limburg (consisting of the Province of Limburg minus its two major cities, Maastricht and Venlo, so as to not exceed the 150,000 number).

To clarify the position of the Grand Duchy of Luxembourg and the Duchy of Limburg, which were possessions of the Dutch king but also member states of the Confederation, the Second Treaty of London in 1867 affirmed that Limburg was an "integral part of the Kingdom of the Netherlands", while Luxembourg was and had been an independent state in personal union with the Kingdom of the Netherlands since 1839.