 In his early twenties, during probation work at the University of Belgrade, he engaged in different students movements that led him to fight in the Spanish Civil War and World War II.He was an officer in the International Brigades from 1937 until he was captured after Franco's victory in April 1939 and incarcerated in the prison of Castres.He escaped in 1942 with 36 other Brigadists and joined the French Resistance.