 After the war, he was convicted by the Allies of "spoliation and plunder", but released almost immediately, and continued his career as a political lobbyist and business executive, becoming chairman of a Swiss chemical company.Ilgner came from an established military family, with his father and grandfather both officers, and followed in their footsteps by entering cadet school.He briefly served as a junior officer on the Western Front at the very end of the First World War.