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Domestic reign

Leopold became king in 1865. He explained his goal for his reign in an 1888 letter addressed to his brother, Prince Philippe, Count of Flanders: "the country must be strong, prosperous, therefore have colonies of her own, beautiful and calm."

Leopold's reign was marked by a number of major political developments. The Liberals governed Belgium from 1857 to 1880, and during its final year in power legislated the Frère-Orban Law of 1879. This law created free, secular, compulsory primary schools supported by the state and withdrew all state support from Roman Catholic primary schools. The Catholic Party obtained a parliamentary majority in 1880, and four years later restored state support to Catholic schools. In 1885, various socialist and social democratic groups drew together and formed the Labour Party. Increasing social unrest and the rise of the Labour Party forced the adoption of universal male suffrage in 1893.

During Leopold's reign other social changes were enacted into law. Among these were the right of workers to form labour unions and the abolition of the livret d'ouvrier, an employment record book. Laws against child labour were passed. Children younger than 12 were not allowed to work in factories, children younger than 16 were not allowed to work at night, and women younger than 21 years old were not allowed to work underground. Workers gained the right to be compensated for workplace accidents and were given Sundays off.

Leopold's reluctance to use the Dutch language in public did little to solve the linguistic conflict in Belgium and made him more unpopular than his father with the Flemish Movement. However, his nephew and heir, Prince Baudouin, became something of a hero to the Flemings, and Leopold did make some speeches in Dutch shortly before and after Baudouin's premature death in 1891.

The first revision of the Belgian Constitution came in 1893. Universal male suffrage was introduced, though the effect of this was tempered by plural voting. The eligibility requirements for the Senate were reduced, and elections would be based on a system of proportional representation, which continues to this day. Leopold pushed strongly to enable a royal referendum, whereby the king would have the power to consult the electorate directly on an issue, and use his veto according to the results of the referendum. The proposal was rejected, as it would have given the king the power to override the elected government. Leopold was so disappointed that he considered abdication.

Leopold emphasized military defence as the basis of neutrality, and strove to make Belgium less vulnerable militarily. He achieved the construction of defensive fortresses at Liège, at Namur and at Antwerp. During the Franco-Prussian War, he managed to preserve Belgium's neutrality in a period of unusual difficulty and danger. Leopold pushed for a reform in military service, but he was unable to obtain one until he was on his deathbed. The Belgian army was a combination of volunteers and a lottery, and it was possible for men to pay for substitutes for service. This was replaced by a system in which one son in every family would have to serve in the military. According to historian Jean Stengers, Leopold II’s imperialism was driven by economic advantage rather than political grandeur. Leopold sought to maximize profit through efficient exploitation, including forced labor and direct revenue. However, Stengers emphasizes that Leopold’s voracity was not solely for personal enrichment; it was also rooted in patriotism—a desire to ensure Belgium’s prosperity and embellishment.