When diplomatic efforts between Britain and Germany failed to end Hitler's attack on Poland - in early September, 1939 - Neville Chamberlain (the Britain's Prime Minister) announced that Britain and Germany were at war.
It was a personally difficult time for Chamberlain. He had attempted to avoid a conflict, but events in Poland proved Chamberlain's assessment of Hitler was wrong.
He made this announcement on Sunday morning, the 3rd of September, 1939. It is preceded by brief introductory comments regarding the situation in Poland.
The following is a transcript of Chamberlain's brief speech:
I am speaking to you from the Cabinet Room at 10 Downing Street.
This morning the British Ambassador in Berlin handed the German Government a final note stating that, unless we hear 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.
You can imagine what a bitter blow it is to me that all my long struggle to win peace has failed. Yet I cannot believe that there is anything more or anything different that I could have done and that would have been more successful.
Up to the very last it would have been quite possible to have arranged a peaceful and honourable settlement between Germany and Poland, but Hitler would not have it. He had evidently made up his mind to attack Poland, whatever happened, and although he now says he put forward reasonable proposals which were rejected by the Poles, that is not a true statement.
The proposals were never shown to the Poles, nor to us, and though they were announced in a German broadcast on Thursday night, Hitler did not wait to hear comments on them but ordered his troops to cross the Polish frontier the next morning.
His action shows convincingly that there is no chance of expecting that this man will ever give up his practice of using force to gain his will. He can only be stopped by force.
We and France are today, in fulfilment of our obligations, going to the aid of Poland, who is so bravely resisting this wicked and unprovoked attack upon her people. We have a clear conscience - we have done all that any country could do to establish peace.
The situation in which no word given by Germany's ruler could be trusted, and no people or country could feel itself safe, has become intolerable. And now that we have resolved to finish it I know that you will play your part with calmness and courage.
At such a moment as this the assurances of support which we have received from the empire are a source of profound encouragement to us.
When I have finished speaking, certain detailed announcements will be made on behalf of the government. Give these your closest attention. The government have made plans under which it will be possible to carry on work of the nation in the days of stress and strain that may be ahead...
Now may God bless you all. May He defend the right. For it is evil things that we shall be fighting against - brute force, bad faith, injustice, oppression and persecution - and against them I am certain that right will prevail.
Britain's early involvement in the war did not help Poland. Hitler had secretly agreed with Joseph Stalin that Soviet forces would march into Poland from the east. That is exactly what happened on the 17th of September, and Poland was effectively squeezed from both sides.
Warsaw surrendered ten days later and, by the 6th of October, Poland became an occupied nation.
BBC Broadcast, September 3, 1939.
Online, courtesy Archive.org.