In 1579 the union was fatally weakened by the defection of the Roman Catholic Walloon provinces in the Union of Arras. By 1588 the Spanish, under Alexander Farnese, Duke of Parma, had reconquered the southern Low Countries leaving only Ostend as a major rebel enclave along the coast and stood poised for a death blow against the nascent Dutch Republic in the north. Spain's concurrent enterprises against England and France at this time, however, allowed the Republic to begin a highly successful counter-offensive under Maurice of Orange which lasted from 1590–1600, known as the "Ten Glory Years".