Some causes of the Belgian revolt in a nutshell.
The union of Belgium and the Netherlands into the United Kingdom of the Netherlands after the Congress of Vienna between 1813-1814 brought two very different states together. The northern king and gentry saw the southern provinces as a gain of Dutch territory. Belgium was catholic and had a strong catholic hierarchy, the United Provinces were calvinist ever since the start of the spanish revolt in 1568. Whene Willem I tried to nationalise the appointment of catholic priest in the 1820s people got pissed off. Also belgium was more industrialised more modern and had a larger population then the Netherlands. And ofcourse the belgian elite did not like to be treated as inferior. On top of all this Willem I used a very complicated financial system to fund public works(and his own wallet) which was generally miststrusted by the belgians. Influenced by the Enlightenment and the recent dethronement of the French king Charles X the revolt kicked off in august 1830. Militarily the revolt was defeated by the Dutch but because of some stupid Dutch politcal moves the Belgians soon gained support from the French and got their own independant country.
Quite a bad summary read wiki or a book .