Before the conquest, the Romans had annexed lands to the southeast extending beyond the Rhine River. They penetrated the Netherlands region mainly to control the several mouths of the Rhine, which were then farther to the north than they are now. Under Roman rule, general peace and prosperity prevailed for more than 250 years. Roman traders entered the area freely, selling products from Italy and Gaul. The Romans built temples, established a number of large farms, and introduced their civilization to the region. About ad 300 the hold by the Romans began to weaken, and nonindigenous German tribes pushed into the area from the east. The Frisians, in the north, held their ground, but Saxons occupied the eastern part of the region, and the Franks moved into the west and south.

The immediate political significance of the union was that it dovetailed with the Union of Arras, concluded earlier in the month, which began the reconciliation of the southerners with King Philip II of Spain. The two “unions,” parallel but opposite, thus undermined the policy of Prince William of Orange of collaboration between Roman Catholics and Calvinists throughout the Low Countries in resistance to the Spanish domination, which required mutual toleration among the religions. But it took some time before the “general union,” with its base in the States-General at Brussels, fell apart irrevocably. For another half decade the prince struggled to keep intact the broader union and at the same time to assure its military and political support from abroad. Although Archduke Matthias of Habsburg, named governor-general by the States-General in 1577 after the deposition of Don Juan, remained the formal head of state until 1581, the prince continued to exercise his leadership. That the prince was the head and heart of the rebellion was recognized by Philip II in 1580 when he put him under the ban of outlawry. William's Apology in defense of his conduct was followed in 1581 by the Act of Abjuration (Akte van Afzwering) by which the States-General declared that Philip had forfeited his sovereignty over the provinces by his persistent tyranny.

The political disaffection between the Low Countries and Spain coincided with the Protestant revolt against the Roman Catholic church, which was the state church of Spain. Calvinism, a Protestant movement, rapidly gained ground during this period; its adherents established in the Low Countries a well-organized church that was prepared to challenge the Roman Catholic church, particularly the Inquisition, a church institution that sought to control heresy. In 1566 riots in which mobs destroyed images in Catholic churches spread across the country. In response, a wrathful Philip sent to the Netherlands Spanish troops commanded by Fernando Álvarez de Toledo, Third Duke of Alba. The excessively harsh policies of the duke and of the Inquisition resulted in open revolt in the Low Countries. William I, the Silent, prince of Orange, who was one of the principal noblemen of the region, led the revolt.