Answer based on context:

Henry XVI already had a dispute with Louis VII's father Stephen III. On 17 April 1414, Henry and other enemies of Louis VII founded the Parakeet Society.  On 8 July 1415, the society was changed into the League of Constance, an alliance for mutual defense against Louis VII.  In 1417 in Constance, Louis insulted Henry by calling him "the son of a cook". When Louis then accused Henry of having shed human blood, Henry and fifteen of his followers physically attacked Louis and injured him severely. After this attack, Louis described Henry as a pluethunt , which did little to defuse the conflict. Henry XVI evaded punishment for the attack on Louis VII only through the intercession of Frederick of Brandenburg and his cousins Dukes Ernest and William III in Munich and especially by paying 6000 guilders to King Sigismund.  Henry XVI wanted revenge. The conflict escalated into a war when an army from Bavaria-Ingolstadt burned down the castle of the Burgrave of Nuremberg. John III, who had succeeded his brother William II as Duke of Bavaria-Straubing in 1418, remained neutral.

When was the League of Constance originally formed?
On 17 April 1414