Complex sentence: The cemetery was originally established by the French Army's 15th Hopital D'Evacuation between autumn 1914 and early summer 1915 for casualties from the Western Front who had been treated at Lijssenthoek but had not survive their wounds.
Split into simpler sentences: The cemetery was originally established at the start of the war by the French Army's 15th Hopital D'Evacuation. Between autumn 1914 and early summer 1915, this unit began to bury casualties from the Western Front who had been treated at their Lijssenthoek field hospital but had not survived their wounds.