[2] According to Alain Derville, John served the King of England in a military capacity before returning to Artois.
According to the chronicler Philippe Mousket, he led the armies of Count Ferdinand of Flanders against Duke Henry I of Brabant in 1227 in support of the lord of Enghien.
[1] John's marriage the following year was probably meant to seal an alliance between Elisabeth and Ferdinand against Philip Hurepel, who was challenging Blanche of Castile for the regency of France.
The marriage was within the prohibited degree of kinship, but the attempts of Enguerrand of Coucy and Elisabeth's son Hugh V to have it annulled failed.
According to William of Andres, Ferdinand invaded Saint-Pol in 1229, but was defeated by Elisabeth's son Hugh, an ally of Hurepel.