further in the Spanish Netherlands. He assumed command of operations at Grave, which had been besieged since 28 June. Grave surrendered on 27 October. The Dutch were split by internal disputes; the powerful Amsterdam mercantile body were anxious to end an expensive war once their commercial interests were secured, while William saw France as a long-term threat that had to be defeated. This conflict increased once ending the war became a distinct possibility when Grave was captured in October 1674, leaving only Maastricht. On both sides, the last years of the war saw minimal return for their investment of men and money. The French were preparing a major offensive, however, at the end of 1676. Intended to capture Valenciennes, Cambrai and Saint-Omer in the Spanish Netherlands. Louis believed this would deprive the Dutch regents of the courage to continue the war any longer. In this, however, he was mistaken. The impending French offensive actually led to an intensification of Dutch-Spanish cooperation. Still, the French offensive of 1677 was a success. The Spaniards found it difficult to raise enough troops due to financial constraints and the Allies were defeated in the Battle of Cassel. This meant that they could not prevent the cities from falling into French hands. The French then took a defensive posture, afraid that more success would force England to intervene on the side of the Allies. The peace talks that began at Nijmegen in 1676 were given a greater sense of urgency in November 1677 when William married his cousin Mary, Charles II of England's niece. An Anglo-Dutch defensive alliance followed in March 1678, although English troops did not arrive in significant numbers until late May. Louis seized this opportunity to improve his negotiating position and captured Ypres and Ghent in early March, before signing a peace treaty with the Dutch on 10 August. The Battle of Saint-Denis was fought three days later on 13 August, when a combined Dutch-Spanish force under William attacked the French army under Luxembourg. Luxembourg withdrew and William thus ensured Mons would remain in Spanish hands. On 19 August, Spain and France agreed an armistice, followed by a formal peace treaty on 17 September. The war had seen the rebirth of the Dutch States Army as one of the most disciplined and best-trained European armed forces. That this had not been enough to keep France from making conquests in the Spanish Netherlands