The United Kingdom of the Netherlands (Dutch: Verenigd Koninkrijk der Nederlanden; French: Royaume-Uni des Pays-Bas) is the unofficial name given to the Kingdom of the Netherlands as it existed between 1815 and 1839. The United Netherlands was created in the aftermath of the Napoleonic Wars through the fusion of territories that had belonged to the former Dutch Republic, Austrian Netherlands, and Prince-Bishopric of Liège in order to form a buffer state between the major European powers. The polity was a constitutional monarchy, ruled by William I of the House of Orange-Nassau.
The polity collapsed in 1830 with the outbreak of the Belgian Revolution. With the de facto secession of Belgium, the Netherlands was left as a rump state and refused to recognise Belgian independence until 1839 when the Treaty of London was signed, fixing the border between the two states and guaranteeing Belgian independence and neutrality as the Kingdom of Belgium.