When the war began on 1 September 1939, Franklin D. Roosevelt, President of the neutral United States, issued an appeal to the major belligerents to confine their air raids to military targets. The French and British agreed to abide by the request, provided "that these same rules of warfare will be scrupulously observed by all of their opponents". British policy was to restrict bombing to military targets and infrastructure, such as ports and railways which were of military importance. While acknowledging that bombing Germany would cause civilian casualties, the British government renounced deliberate bombing of civilian property (outside combat zones) as a military tactic. The British abandoned this policy at the end of the "Phoney War", or "Sitzkrieg", on 15 May 1940, one day after the Rotterdam Blitz.