By 1944 the stress of the war had taken a serious toll on Bishop's health, and he resigned his post in the RCAF to return to private enterprise in Montreal, Quebec, before retiring in 1952. His son later commented that he looked 70 years old on his 50th birthday in 1944. However, Bishop remained active in the aviation world, predicting the phenomenal growth of commercial aviation postwar. His efforts to bring some organization to the nascent field led to the formation of the International Civil Aviation Organization (ICAO) in Montreal. He wrote a second book at this time, "Winged Peace", advocating international control of global air power.