Philip's stern Counter-Reformation measures sparked the Dutch Revolt in the mainly Calvinist Netherlandish provinces, which led to the outbreak of the Eighty Years' War in 1568. In January 1579 the seven northern provinces formed the Protestant Union of Utrecht, which declared independence from the Spanish branch of the Habsburgs as the Republic of the Seven United Netherlands by the 1581 Act of Abjuration. The Spanish branch of the Habsburgs could retain the rule only over the partly Catholic Southern Netherlands, completed after the Fall of Antwerp in 1585.