The state of war was announced to the British public in an 11 AM radio broadcast by the prime minister Neville Chamberlain.
This morning, the British ambassador in Berlin handed the German government a final note stating that unless we heard from them by 11 o'clock that they were prepared at once to withdraw their troops from Poland, a state of war would exist between us. I have to tell you now that no such undertaking has been received, and that consequently this country is at war with Germany.[2]
Negotiations between the Allied powers regarding post-war Europe started on 18 January 1919 in the Salle de l'Horloge at the French Foreign Ministry on the Quai d'Orsay in Paris. Seventy delegates from 27 nations participated in the negotiations. The opposing nations of the German Empire and the Austro-Hungarian Empire were excluded from the negotiations. At first a "Council of Ten" comprising two delegates each from Britain, France, the United States, Italy and Japan met officially to decide the peace terms. It became the "Big Four" when Japan dropped out and the top person from each of the other four nations met in 145 closed sessions to make all the major decisions to be ratified by the entire assembly. In June 1919, the Allies declared that war would resume if the German government did not sign the treaty they had agreed to among themselves. The government headed by Philipp Scheidemann was unable to agree on a common position, and Scheidemann himself resigned rather than agree to sign the treaty. Gustav Bauer, the head of the new government, sent a telegram stating his intention to sign the treaty if certain articles were withdrawn, including articles 227, 230 and 231. In response, the Allies issued an ultimatum stating that Germany would have to accept the treaty or face an invasion of Allied forces across the Rhine within 24 hours. On 23 June 1919, Bauer capitulated and sent a second telegram with a confirmation that a German delegation would arrive shortly to sign the treaty.
On 30 January 1933, Adolf Hitler was appointed Chancellor of the Reich following a contentious election. Under Hitler's leadership, the Reichstag turned the government into an effective dictatorship under Hitler's oversight on 21 March 1933 with the passage of the Enabling Act of 1933, and the economic hardships were significantly diminished via implementation of new economic and social policies. After five years in power, Hitler annexed Austria, former component of the Austro-Hungarian Empire (allies of the former German Empire), into Germany, despite such an act (specifically, "prohibition on the merging of Austria with Germany without the consent of the League of Nations") being banned by both the Treaty of Saint-Germain-en-Laye and the Treaty of Versailles. In early November 1938, the First Vienna Award was signed, allowing Germany to seize the Sudetenland, a German-speaking area of Czechoslovakia which had been a part of the German Empire-allied Austro-Hungarian Empire. Soon after, Germany invaded the rest of Czechoslovakia and also gained Memelland (part of the former German Empire from 1871–1920) through the 1939 German ultimatum to Lithuania.
Two Western powers, the United Kingdom and France, gave guarantees to Poland that they would declare war if Polish independence came under threat, as presented in a statement to the House of Commons by the British Prime Minister Neville Chamberlain on 31 March 1939 (formalized by the British on 6 April 1939; not ratified until 4 September 1939 by the French):
... in the event of any action which clearly threatened Polish independence, and which the Polish Government accordingly considered it vital to resist with their national forces, His Majesty's Government would feel themselves bound at once to lend the Polish Government all support in their power. They have given the Polish Government an assurance to this effect.
I may add that the French Government have authorised me to make it plain that they stand in the same position in this matter as do His Majesty's Government.[5]
After the declaration of war
The Royal Navy initiated a naval blockade of Germany on 4 September.
Although Britain and France honoured these guarantees by declaring war two days after Germany's invasion of Poland on 1 September 1939,[6] and the dominions of the British Empire quickly followed suit, so little practical assistance was given to Poland, which was soon defeated, that in its early stages the war declared by Britain and France was described as a "Phoney War".
Further, neither the British Empire nor the French ever declared war upon the Soviet Union, which invaded Poland on 17 September 1939 (16 days after Nazi Germany invaded from the West). The Polish ambassador in London, Edward Bernard Raczyński, contacted the British Foreign Office to point out that clause 1(b) of the agreement, which concerned an "aggression by a European power" on Poland, should apply to the Soviet invasion. Foreign SecretaryLord Halifax responded that the obligation of British Government towards Poland arising out of the Anglo-Polish Agreement was restricted to Germany, according to the first clause of the secret protocol.[7] The Soviet Union held sway over the former Polish territory at the war's conclusion, having become a part of the Allies in the course of World War II. At the insistence of Joseph Stalin, the post-war Yalta Conference in 1945 sanctioned the formation of a new provisional pro-Communist coalition government in Moscow, which ignored the Polish government-in-exile based in London.
