It’s a tale as old as empire. A group of small, quasi-related states band together to fight against their imperial overlords. Could be the Rebellion in Star Wars. Could be the founding of the United States. Could be most stories dealing with decolonization, really. But no. This particular fight occurred long before those (or maybe a long time after, in a galaxy much closer to home. Time is weird). Parts of the Netherlands first unified into what would eventually become an independent country on, 23 January 1579, signing the treaty known as the Union in Utrecht.
The Low Countries, as Netherlands literally means, has been inhabited since prehistoric times. Like much of northern Europe, the Netherlands also has ties to Celtic and Germanic tribes before becoming part of the Holy Roman Empire (which, despite Voltaire making a joke that it was not holy, Roman, or an empire was likely all three, depending on your point of view).
Through the intermarriages amongst a small group of families that characterizes European nobility, the territory was brought under Hapsburg (sometimes spelled Habsburg) control. This intermingling was epitomized in Charles V who, as a Hapsburg heir, was King of Spain and Holy Roman Emperor in the early- and mid-16th century. Under Charles V the Hapsburgs controlled roughly a third of all Europe, including what would eventually become Spain, most of southern Italy and Sicily, Austria, Hungary, parts of Germany, and the Netherlands. By comparison, France, Britain, the Russian Empire, and the Ottomans controlled most of the rest of the continent. There were many wars and conflicts between these great powers (Switzerland continued to remain firmly neutral), with ever-shifting alliances. Europe in the late medieval and early modern period was a mess; it’s great!
Religion was one of the dominant factors of allyship. Most of southern Europe, including Spain under Charles and his son Philip II, was Catholic. Much of northern Europe, including areas of the Netherlands, was Protestant (in one of its many, many denominations). Tensions all across Europe rose, especially since both Charles and Philip wanted all of their domains to be Catholic. The Calvinists, a branch of Protestants, were a very vocal objector to this attempted overlordship. After a brief period of peaceful protests, armed fighting eventually broke out in 1566. This conflict eventually escalated further and became known as the Eighty Years War.
Under Hapsburg rule, the Netherlands was broken into seventeen provinces which covered most of present-day Belgium, Netherlands, Luxembourg, and bits of northern France. After years of fighting, two of the provinces (those closest to still-Catholic France) declared their loyalty to Catholic Spain. In response, the Protestant northern provinces of Holland, Zeeland, Utrecht, and portions of Groningen signed a formal treaty, the Union of Utrecht, declaring their union. They were later joined by the cities of Ghent, Ypres, Antwerp, Breda, Lier, Bruges, and Brussels, as well as the provinces of Friesland, Overijssel and Drenthe.
Though it was not intended to serve as a formal new nation, it did act as a de facto announcement of independence and a quasi-constitution. One of its key points was providing a limited form of religious tolerance in the union. This tolerance was nowhere near absolute, and each province could set its own rules. They did basically agree that the Dutch Reformed Church enjoyed a privileged position, while Catholicism was banned completely. Other Protestant sects and Jews had various restrictions. Still, even this limited tolerance was almost unheard of during the period.
While the Union of Utrecht was not a formal state, the Act of Abjuration, signed on 26 July 1581, declared an official independent Dutch Republic. That Republic continued to fight the Hapsburgs during the Eighty Years War, with peace only declared in 1648. The Republic lasted until 1795 when it became a puppet kingdom under Napoleon, before becoming its own independent kingdom again in 1815. In 1830, the southern provinces staged their own rebellion, forming Belgium, and in 1890 Luxembourg also became an independent realm.
Today the Netherlands is considered one of the most tolerant (at least in terms of religion and some cultural norms) in all the world. Utrecht, where the Union was signed, is a quaint town. I used to live there. I don’t think I did ever climb the 465 steps to the top of the Dom Tower, though.