the creation of Belgium. Accession of King Leopold In November 1830, the National Congress of Belgium was established to create a constitution for the new state. The Congress decided that Belgium would be a popular, constitutional monarchy. On 7 February 1831, the Belgian Constitution was proclaimed. However, no actual monarch yet sat on the throne. The Congress refused to consider any candidate from the Dutch ruling house of Orange-Nassau. Eventually the Congress drew up a shortlist of three candidates, all of whom were French. This itself led to political opposition, and Leopold of Saxe-Coburg, who had been considered at an early stage but dropped due to French opposition, was proposed again. On 22 April 1831, Leopold was approached by a Belgian delegation at Marlborough House to officially offer him the throne. At first reluctant to accept, he eventually took up the offer, and after an enthusiastic popular welcome on his way to Brussels, Leopold I of Belgium took his oath as king on 21 July 1831. 21 July is generally used to mark the end of the revolution and the start of the Kingdom of Belgium. It is celebrated each year as Belgian National Day. Post-independence Ten Days' Campaign King William was not satisfied with the settlement drawn up in London and did not accept Belgium's claim of independence: it divided his kingdom and drastically affected his Treasury. From 2–12 August 1831 the Dutch army, headed by the Dutch princes, invaded Belgium, in the so-called "Ten Days' Campaign", and defeated a makeshift Belgian force near Hasselt and Leuven. Only the appearance of a French army under Marshal Gérard caused the Dutch to stop their advance. While the victorious initial campaign gave the Dutch an advantageous position in subsequent negotiations, the Dutch were compelled to agree to an indefinite armistice, although they continued to hold the Antwerp Citadel and occasionally bombarded the city until French forces forced them out in December 1832. William I would refuse to recognize a Belgian state until April 1839, when he had to yield under pressure by the Treaty of London and reluctantly recognized a border which, with the exception of Limburg and Luxembourg, was basically the border of 1790. 1839 Treaty of London On 19 April 1839 the Treaty of London signed by the European powers (including the Netherlands) recognized Belgium as an independent and neutral country comprising West Flanders, East Flanders, Brabant, Antwerp, Hainaut,