Complex sentence: Zervas was a fanatic Venizelist, and in 1916 he was among the very first to join the venizelist Movement of National Defence in Thessaloniki, and was distinguished in many battles of the Macedonian front during World War I, being promoted to Major.
Split into simpler sentences: Zervas was a fanatic Venizelist, and in 1916 he was among the very first to join the venizelist Movement of National Defence in Thessaloniki. He served with distinction in many battles of the Macedonian front during World War I, being eventually promoted to Major.