William at the head of 20,000 German and 3000 Walloon mercenaries actually entered Gelderland (July 7), captured Roeremonde and then marched into Brabant.

Here (July 19) the news reached him of the complete defeat and annihilation of the raw levies of Genlis by Toledo's veteran troops.

Hampered by lack of funds William now, as throughout his life, showed himself to be lacking in the higher qualities of military leadership.

With an ill-paid mercenary force time was a factor of primary importance, nevertheless the prince made no effort to move from his encampment near Roeremonde for some five weeks.
Meanwhile his troops got out of hand and committed many excesses, and when, on August 27, he set out once more to march westwards, he found to his disappointment that there was no popular rising in his favour.
Louvain and Brussels shut their gates, and though Mechlin, Termonde and a few other places surrendered, the prince saw only too plainly that his advance into Flanders would not bring about the relief of Mons.

All his plans had gone awry.