At the Congress of Vienna, in 1815, Belgium (The Southern Netherlands) and the Northern Netherlands (Holland) were united to form one State, ruled by King William I. There was protest from the Catholics against the interference of the protestant king in clerical matters, from the Liberals whom asked for more freedom. Both drew up a concerted programme of demands in 1828. The association between Catholics and Liberals was called unionism.
After a series of incidents, the revolution erupted in Brussels in 1830. William I sent in his troops, but they were expelled on September 27th, 1830. The rebels received support from volunteers outside the city of Brussels. Following this rising Belgium separated from the Northern Netherlands. A provisional government declared independence on October 4th, 1830. On November 3th of the same year an electorate of 30,000 men who paid a given level of taxes or who had special qualification selected a National Congress. On February 7th, 1831 the national congress adopted a constitution, which for its time, was very progressive.