Although the French missed an opportunity for a rout by delaying their pursuit to plunder the Allies' abandoned baggage, Cassel was one of the most comprehensive victories of the war.

However, the Dutch position stabilised, while concern at French gains brought them support from Frederick William, Elector of Brandenburg, Emperor Leopold and Habsburg Spain.

[12] The plan for 1677 was to take Valenciennes, Cambrai and Saint-Omer, completing the French frontière de fer or iron border; Louis calculated that this would leave the Dutch little reason to continue fighting.

[14] Delayed by lack of money and supplies, the Dutch-Spanish force reached Mont-Cassel on 9 April, near the French-held town of Cassel, about 15 km (9 mi) west of Saint-Omer.

A charge led by the Prince of Nassau threw the French back across the river; the Dutch cavalry ran into heavy artillery fire, retreated to the far side of Mont-Cassel, and played no further part in the battle.

[17] A simultaneous attack by Humières on the right was also successful, but the French centre was over-run by infantry under Prince Georg Friedrich of Waldeck and the line only re-established after a charge led by Orléans himself.

Luxembourg avoided battle, forcing William to besiege Charleroi instead; this was unsuccessful and the French followed up by taking Saint-Ghislain in December, but it demonstrated the Dutch capacity to fight on.

[18] English public opinion was strongly anti-French and Cassel led to pressure from Parliament to intervene on behalf of the Dutch, forcing Louis to downplay this success.

The Dutch were reluctant to continue the war but restoring the Spanish Netherlands as a buffer zone became even more important after the disasters of 1672, while their position was improved by William's marriage in November 1677 to Charles II's niece, Mary.

[20] The 1678 Treaties of Nijmegen reset France's northern border, Spain ceding Saint-Omer, Cassel, Aire, Ypres, Cambrai, Valenciennes and Maubeuge.