Excerpts from Books and Wikipedia
"The Union of Utrecht, signed on January 23, 1579, was limited to the seven northern provinces of the Netherlands and declared their independence from Spanish rule. . . . However, without effective aid from England or France, the rebels hardly posed a military challenge to Spain. The Union of Utrecht was really a holding operation designed to present a united front to the outside world and foster support. As the tension escalated, the revolt's leader, William the Silent, issued the Oath of Abjuration. The oath was effectively a 'Declaration of Independence' since the Union of Utrecht had stopped short of renouncing the king of Spain." [Furtado: 1001 Days]