Complex sentence: Edward kept up his part of the deal and turned over his continental estates to the French but Philip used the pretext that the English king had refused his summons in order to strip Edward of all his possessions in France, thereby initiating hostilities with England.
Split into simpler sentences: Edward kept up his part of the deal and turned over his continental estates to the French. However, Philip used the pretext that the English king had refused his summons in order to strip Edward of all his possessions in France, thereby initiating hostilities with England.