William I (Willem Frederik; 24 August 1772 – 12 December 1843) was King of the Netherlands and Grand Duke of Luxembourg from 1815 until his abdication in 1840.

His reign saw the adoption of a new constitution, which granted him extensive powers, and he was a strong proponent of economic development, founding several universities and promoting trade.

However, his efforts to impose the Reformed faith and the Dutch language in the southern provinces, combined with economic grievances, sparked the Belgian Revolution in 1830.

As compensation for the loss of his father's possessions in the Low Countries, William was appointed ruler of the newly created Principality of Nassau-Orange-Fulda in 1803.

With the death of his father in 1806, he became Prince of Orange and ruler of the Principality of Orange-Nassau, which he also lost the same year after the dissolution of the Holy Roman Empire and subsequent creation of the Confederation of the Rhine.

In 1813, following Napoleon's defeat at Leipzig, the Orange-Nassau territories were restored to William; he also accepted the offer to become Sovereign Prince of the United Netherlands.

In the same year, he concluded a treaty with King Frederick William III in which he ceded the Orange-Nassau to Prussia in exchange for becoming the new grand duke of Luxembourg.

As king, he adopted a new constitution, presided over strong economic and industrial progress, promoted trade and founded the universities of Leuven, Ghent and Liège.

The imposition of the Reformed faith and the Dutch language, as well as feelings of economic inequity, caused widespread resentment in the southern provinces and led to the outbreak of the Belgian Revolution in 1830.

William's disapproval of changes to the constitution, the loss of Belgium and his intention to marry Henrietta d'Oultremont, a Roman Catholic, led to his decision to abdicate in 1840.

In Berlin on 1 October 1791, William married his maternal first cousin (Frederica Louisa) Wilhelmina of Prussia, born in Potsdam.

In 1790 he visited a number of foreign courts like the one in Nassau and the Prussian capital Berlin, where he first met his future wife.

In May 1794 he had replaced general Kaunitz as commander of the combined Austro-Dutch forces on the instigation of Emperor Francis II who apparently had a high opinion of him.

Despite a well-executed attack by William on the French left, the allied army under Coburg was finally defeated at the Battle of Fleurus.

When in the winter of 1794–95 the rivers in the Rhine delta froze over, the French breached the southern Hollandic Water Line and the situation became militarily untenable.

[2]: 341–365, 374–404, 412 Soon after the departure to Britain the hereditary prince went back to the continent, where his brother was assembling former members of the States Army in Osnabrück for a planned invasion into the Batavian Republic in the summer of 1795.

[4]: 241–265 When peace was concluded between Great Britain and the French Republic under First Consul Napoleon Bonaparte the Orange exiles were at their nadir.

Dynastic considerations of marriage between the royal houses of Great Britain and the Netherlands, assured British approval.

In the ensuing power vacuum a number of former Orangist politicians and former Patriots formed a provisional government in November 1813.

[3]: 634–642 After having been invited by the Triumvirate of 1813, on 30 November 1813 William disembarked from HMS Warrior and landed at Scheveningen beach, only a few yards from the place where he had left the country with his father 18 years before, and on 6 December the provisional government offered him the title of king.

In August 1814, he was appointed Governor-General of the former Austrian Netherlands and the Prince-Bishopric of Liège (more or less modern-day Belgium) by the Allied Powers who occupied that country, ruling them on behalf of Prussia.

The Great Powers had already agreed via the secret Eight Articles of London to unite the Low Countries into a single kingdom, it was believed that this would help keep France in check.

With the de facto addition of the Austrian Netherlands and Luxembourg to his realm, William had fulfilled his family's three-century dream of uniting the Low Countries.

Feeling threatened by Napoleon, who had escaped from Elba, William proclaimed the Netherlands a kingdom on 16 March 1815 at the urging of the powers gathered at the Congress of Vienna.

In 1822, he founded the Algemeene Nederlandsche Maatschappij ter Begunstiging van de Volksvlijt, which would become one of the most important institutions of Belgium after its independence.

Dutch was imposed as the official language in (the Dutch-speaking region of) Flanders; this angered French-speaking aristocrats and industrial workers.

In August 1830 Daniel Auber's opera La muette de Portici, about the repression of Neapolitans, was staged in Brussels.

Rioting ensued, chiefly aimed at the kingdom's unpopular justice minister, Cornelis Felix van Maanen, who lived in Brussels.

Although initially victorious in this Ten Days' Campaign, the Royal Netherlands Army was forced to retreat after the threat of French intervention.

This, the disappointment about the loss of Belgium, and his intention to marry Henrietta d'Oultremont (paradoxically both "Belgian" and Roman Catholic) made him wish to abdicate.