In 1635 France and the Dutch Republic formed an alliance against Spain with the objective of conquering and partitioning the Spanish Netherlands. They invaded on two fronts in June 1635, but soon the Spanish forces regained the initiative against the combined Franco-Dutch army, which was ignominiously driven to the Dutch border. There Spain managed to capture the strategic fortress of Schenkenschans by surprise. This forced the Dutch to enter upon a long and costly siege of that fortress that occupied the Dutch army for nine months. After the recapture of Schenkenschans in April 1636, the Spanish commander, the Cardinal-Infante Ferdinand of Spain, shifted his focus to France. This required that the Army of Flanders move away from the Dutch border; therefore the military threat Spain posed to the Dutch Republic lessened. In the summer of 1636 the Cardinal-Infante reached as far as Corbie, but this city was retaken by the French in November, and at the end of the year Spain had lost most of its gains. For the campaign of 1637 Olivares planned a renewed offensive against France. In Brussels the Cardinal-Infante actually would have preferred an offensive against the Dutch, but reluctantly agreed to take part in the three-pronged invasion of France that summer. He therefore started to mass his forces on the French border when word came that the Dutch had suddenly invested the city of Breda with a besieging army of 18,000. Breda was the capital city of the baronial fief that had once been the crown jewel in the Dutch estates of the Nassau family in the Habsburg Netherlands before the war started. Frederick Henry had therefore a personal interest in recapturing the city and its surroundings.
The siege
The siege was preceded by an attempt to surprise the garrison on 21 July 1637 by Dutch cavalry under Henry Casimir I of Nassau-Dietz. However, the gates were closed in time and the Dutch skirmishers driven back. The Dutch then from 23 July on first captured a number of villages around the city and then started to dig a double line of circumvallation that would eventually reach a circumference of 34 km. An outer contravallation defended the besiegers from outside interference, and outside this area the low-lying countryside was inundated by damming a few rivers. Unlike the strategy adopted by Ambrosio Spinola at Breda in 1624–25, Frederick Henry did not plan on a passive siege, aimed at starving the fortress, but intended a more aggressive approach. The Spanish attempt at relief that the Cardinal-Infante soon launched was unable to dislodge the besiegers. He therefore lifted his siege of the besiegers and moved with his army to the valley of the Meuse, where he took Roermond and Venlo from the Dutch, a considerable loss. . Undistracted, the besiegers meanwhile started digging covered trenches inward from the circumvallation line toward the hornworks of the fortress, which had been constructed by the Dutch themselves on the model of a star fort. Two of these trenches were dug toward the Ginnekenpoort, one by French, the other by English mercenaries. The French finished their work on 27 August, the English one day later. Fascines were used to fill the moat. The French and English scaled the walls of the hornwork on 1 September. That same night, the French ambassador Girard de Charnacé, who commanded a French regiment of the besiegers, was adventitiously killed by a bullet to the head. The besiegers then started mining the hornwork, and on 7 September the mine was blown, breaching the walls. George Monk, later first Duke of Albermarle, then a captain in Dutch service, was first in the breach. The hornwork was taken. However, a few days later a different mine misfired, and another attack was repelled with great loss of life among the Dutch and Scottish attackers. Nevertheless, the defenders now abandoned this part of the outer defense works to the besiegers. On 2 October, count Henry of Nassau managed to take a lunette and ravelin and drive the defenders into the city proper. This meant that the inner city was now open to attack by mines. The garrison knew that the situation was hopeless. Honor having been preserved, the governor, Gomar de Fourdin sued for an honorable surrender on 6 October. The capitulation was signed, and on 11 October the Habsburg garrison left the city with flags flying and drums rolling. They marched off toward Mechelen.
Aftermath
Though Spain almost managed to capture the important fortress of Rheinberg from the Dutch a month after the fall of Breda, the campaign season of 1637 was now over. The next year the Army of Flanders was kept on the defensive by attacks from both France and the Republic. Frederick Henry made an attempt to capture Antwerp, but his advance guard was caught in the open by a crack Spanish force on 20 June 1638 and defeated in the only pitched battle of the second part of the Eighty Years' War at Kallo.
