Complex sentence: Demobilized from World War I in 1917, he moved to Marseille and then to the village of Laudun in the Gard, where he had been on vacation since his childhood as his family owned a house there and a small vineyard.
Split into simpler sentences: Demobilized from World War I in 1917, he moved to Marseille. He then moved to Laudun, Gard, where he had been on vacation since his childhood in the village where his family owned a house and a small vineyard.