economic growth. Feelings of economic inequity were another cause of the Belgian uprising. William was also determined to create a unified people, even though the north and the south had drifted far apart culturally and economically since the south was reconquered by Spain after the Act of Abjuration of 1581. The North was commercial, Protestant and entirely Dutch-speaking; the south was industrial, Roman Catholic and divided between Dutch and French-speakers. Officially, a separation of church and state existed in the kingdom. However, William himself was a strong supporter of the Reformed Church. This led to resentment among the people in the mostly Catholic south. William had also devised controversial language and school policies. Dutch was imposed as the official language in (the Dutch-speaking region of) Flanders; this angered French-speaking aristocrats and industrial workers. Schools throughout the Kingdom were required to instruct students in the Reformed faith and the Dutch language. Many in the South feared that the King sought to extinguish Catholicism and the French language. Revolt of the Southern Provinces In August 1830 Daniel Auber's opera La muette de Portici, about the repression of Neapolitans, was staged in Brussels. Performances of this show seemed to crystallize a sense of nationalism and "Hollandophobia" in Brussels, and spread to the rest of the South. Rioting ensued, chiefly aimed at the kingdom's unpopular justice minister, Cornelis Felix van Maanen, who lived in Brussels. An infuriated William responded by sending troops to repress the riots. However, the riots had spread to other Southern cities. The riots quickly became popular uprisings. An independent state of Belgium emerged out of the 1830 Revolution. The next year, William sent his sons William, the Prince of Orange, and Prince Frederick to invade the new state. Although initially victorious in this Ten Days' Campaign, the Dutch army was forced to retreat after the threat of French intervention. Some support for the Orange dynasty (chiefly among Flemings) persisted for years but the Dutch never regained control over Belgium. William nevertheless continued the war for eight years. His economic successes became overshadowed by a perceived mismanagement of the war effort. High costs of the war came to burden the Dutch economy, fueling public resentment. In 1839, William was forced to end the war. The United Kingdom of the Netherlands was dissolved by the Treaty of London (1839) and the northern part continued as the Kingdom of the Netherlands. It was