He became a national hero in World War I for halting the German advance at Verdun (1916) and later became Commander-in-Chief of French forces (1917). In World War II he concluded an armistice with Nazi Germany after the collapse of French forces in 1940 and established the French government at Vichy (effectively a puppet regime for the Third Reich) until German occupation in 1942. After the war Pétain received a death sentence for collaboration, but this was commuted to life imprisonment.