The territory of Belgium has always been subject to the influence of both the German and Latin world. That brings a cultural pluralism in its wake. So when Belgium was created in 1830-31, that pluralism was already there. It is precisely those differences in language, culture and so on between the various parts of the country that led to the reform of the State.
A major step in the reform of our State were the laws on the use of official languages. These were enacted between 1873 and 1963. Those laws recognise French, Dutch and German as official languages of Belgium. These laws also laid down the use of the languages.
But laws about language alone do not really reform a State. The Constitution needed to be amended. It forms the foundation of the State system. That amendment is referred to as the Revision of the Constitution. With the Revision of the Constitution of 5 May 1993, the Federal State was created. Work started on this federalisation over 40 years ago: first with a wide-ranging reform in 1970, which was intensified in 1980 and continued in 1988-89 and later in 2001 and 2012.