Provocation Offered to Germany
"Germany's complacent acceptance of American violations of neutrality was a surprising feature of the European war between June 1940 and December 1941. In fact, it soon became apparent that Germany did not intend to contribute to a break in diplomatic relations with the United States. American military intervention in Europe during World War I had proved decisive, and Hitler clearly did not want to repeat that experience in World War II.
The important American violations of neutrality during that period included: (1) shipments of considerable amounts of war material to Great Britain, commencing immediately after Dunkirk; (2) the acquisition of overseas bases in British territory, as well as in Greenland and Iceland; (3) the transfer of 50 old destroyers to Great Britain during its state of war with Germany and Italy; (4) the President's broadcast warning to the Axis powers on December 29, 1940, that no dictator could weaken American determination to help Great Britain; (5) the enactment of Lend-Lease on March 11, 1941, which later extended unilateral wartime aid to countries arrayed against the Axis, including Great Britain, Russia, China, Greece, Holland, Norway, and Czechoslovakia; (6) the closure of German and Italian consulates and the freezing of those countries' assets in the United States by Executive Order, in response to Axis attacks on American shipping; (7) the President's explanation in July 1941 that the American occupation of Iceland was undertaken to prevent a possible seizure by Germany; (8) the announcement, also in July 1941, that the United States Navy would keep sea lanes open to Iceland and other advance garrisons, which signified a campaign against German submarines in the mid-Atlantic; and (9) the President's public statement on September 11, 1941, indicating that American naval vessels and planes would fire on Axis ships entering waters vital to American interests."
Rear Admiral Robert Theobald (1954). The final secret of Pearl Harbor;: The Washington contribution to the Japanese attack.