The stadholder, however, was not deterred by the obstacles in his way; and the diplomatic skill and adroitness of Aerssens, aided by his own tact and firmness of will, overcame the scruples of Richelieu.

The opposition of the Estates of Holland, without whose consent no treaty could be ratified, was likewise surmounted.
Adrian Pauw, their leader, was despatched on a special embassy to Paris, and in his absence his influence was undermined, and Jacob Cats was appointed Council-Pensionary in his stead.

In the spring of 1635 a firm alliance was concluded between France and the United Provinces, by which it was agreed that neither power should make peace without the consent of the other, each meanwhile maintaining a field force of 25,000 foot and 5000 horse and dividing conquests in the Southern Netherlands between them.

This treaty was made with the concurrence and strong approval of the Swedish Chancellor, Oxenstierna, and was probably decisive in its effect upon the final issue of the Thirty Years' War.
In the early spring of 1635, therefore, a French force entered the Netherlands and, after defeating Prince Thomas of Savoy at Namur, joined the Dutch army at Maestricht.

Louis XIII had given instructions to the French commanders, Chatillon and de Breze, to place themselves under the orders of the Prince of Orange; and Frederick Henry at the head of 32,000 foot and 9000 horse now entered the enemy's territory and advanced to the neighbourhood of Louvain.