In these circumstances Frederick Henry determined to enter into negotiations with France for the conclusion of an offensive and defensive alliance against Spain, the common enemy.  He had many difficulties to encounter.  The Estates of Holland, though opposed to the terms actually offered by the Brussels government, were also averse to taking any step which shut the door upon hopes of peace.  Richelieu on his side, though ready, as before, to grant subsidies and to permit the enrolment of French regiments for the Dutch service, shrank from committing France to an open espousal of the Protestant side against the Catholic powers.  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.  Here however, owing to the outbreak of disease among his troops, to lack of supplies and to differences of opinion with his French colleagues, the prince determined to retreat.  His action was attended by serious results.  His adversary, the Cardinal Infante Ferdinand, was a wary and skilful general.  He now seized his opportunity, rapidly made himself master of Diest, Gennep, Goch and Limburg, and took by surprise the important fort of Schenck at the junction of the Waal and the Rhine.  Vexed at the loss of a stronghold which guarded two of the main waterways of the land, the stadholder at once laid siege to Schenck.  But the Spanish garrison held out obstinately all through the winter and did not surrender until April 26,1636.  The Dutch army had suffered much from exposure and sickness during this long investment and was compelled to abstain for some months from