In 1939 Kennedy toured Europe, the Soviet Union, the Balkans, and the Middle East in preparation for his Harvard senior honors thesis. He then went to Czechoslovakia and Germany before returning to London on September 1, 1939, the day that Germany invaded Polandto mark the beginning of World War II.
On 1 September 1939, Germany invaded western Poland under the pretext of having been denied claims to the Free City of Danzig and the right to extraterritorial roads across the Polish Corridor, which Germany had ceded under the Versailles Treaty.
On 2 September 1939 (the day after the start of the war), Goebbels and the Council of Ministers proclaimed it illegal to listen to foreign radio stations. Disseminating news from foreign broadcasts could result in the death penalty.
On 3 September 1939, the day Britain declared war on Germany, Chamberlain reappointed Churchill as First Lord of the Admiralty and he joined Chamberlain's war cabinet. Churchill later claimed that the Board of the Admiralty sent a signal to the Fleet: "Winston is back".
The United Kingdom responded with an ultimatum to Germany to cease military operations, and on 3 September, after the ultimatum was ignored, France and Britain, along with their empires, declared war on Germany. The alliance provided no direct military support to Poland, outside of a cautious French probe into the Saarland.
The Polish counter offensive to the west halted the German advance for several days, but it was outflanked and encircled by the Wehrmacht. The Battle of the Bzura fought between 9 and 19 September 1939, It began as a Polish counter-offensive, but ended with German victory, German forces took all of western Poland.
In November 1939, the United States was taking measures to assist China and the Western Allies, and amended the Neutrality Act to allow "cash and carry" purchases by the Allies. Cash and carry was a policy by US President Franklin Delano Roosevelt announced at a joint session of the United States Congress on September 21, 1939, subsequent to the outbreak of war in Europe. It replaced the Neutrality Acts of 1937, by which belligerents could purchase only nonmilitary goods from the United States as long as the recipients paid immediately in cash and assumed all risk in transportation using their own ships.