Complex sentence: Its role during the latter part of World War I on the western front is undetermined, but it remained in France after the armistice until June 1919, arriving back in New York and subsequently demobilized in July.
Split into simpler sentences: Its role during the latter part of World War I on the western front is undetermined. Remained in France after the armistice until June 1919, arrived back in New York and was demobilized in July.