21 July
Belgian National Day (National Day) - the most important holiday of the country - celebrated annually on July 21, starting from 1890, in honor of this significant date. On this day in 1831 as a result of the election of the royal reign of Leopold I (Leopold of Saxe-Coburg). The new king Leopold I took the oath of allegiance to the Belgian Parliament of the Constitution.
In November 1830, elections to the National Congress. The work of the Congress were the adoption of the Declaration of Independence and the Constitution of the country of Belgium. In February 1831, Belgium was declared a constitutional monarchy with a bicameral parliament.
http://www.calend.ru/holidays/0/0/2295/