Union of Utrecht

The Union of Utrecht (Dutch: Unie van Utrecht) is a treaty signed on January 23, 1579 in Utrecht, the Netherlands, unifying the northern provinces of the Netherlands, until then under control of Spain. The Union of Utrecht is regarded as the foundation of the Republic of the Seven United Netherlands, which was not recognised internationally until the Peace of Westphalia in 1648 ended the Eighty Years' War.

The treaty was signed by Holland, Zeeland, Utrecht, Gelderland, Overijssel, Friesland and the province (but not the city) of Groningen. The treaty was a reaction of the Protestant provinces to the 1579 Union of Arras (Dutch: Unie van Atrecht), in which the southern provinces (most of them now part of Belgium) declared their support for the Catholic Spanish.

A number of cities, mainly in Flanders and Brabant, joined the Union after it was signed. However, these cities were conquered by the Spanish army, and did not become a part of the Republic.

The United Provinces still recognized Spanish rule after the Union of Utrecht. However, the Union contributed to the deterioration in the relationship between the provinces and their lord, and in 1581 the United Provinces declared their independence of the king in the Oath of Abjuration.