In the aftermath of Pearl Harbor, and the attack of British possessions in Asia, the Prime Minister of Great Britain, Winston Churchill, wasted no time in recognizing that a state of War existed between the British and the Empire of Japan:
As soon as I heard, last night, that Japan had attacked the United States, I felt it necessary that Parliament should be immediately summoned. It is indispensable to our system of government that Parliament should play its full part in all the important acts of State and at all the crucial moments of the war; and I am glad to see that so many Members have been able to be in their places, despite the shortness of the notice. With the full approval of the nation, and of the Empire, I pledged the word of Great Britain, about a month ago, that should the United States be involved in war with Japan, a British declaration of war would follow within the hour. I, therefore, spoke to President Roosevelt on the Atlantic telephone last night, with a view to arranging the timing of our respective declarations. The President told me that he would this morning send a Message to Congress, which, of course, as is well known, can alone make a declaration of war on behalf of the United States, and I then assured him that we would follow immediately.
However, it soon appeared that British territory in Malaya had also been the object of Japanese attack, and later on it was announced, from Tokyo, that the Japanese High Command—a curious form; not the Imperial Japanese Government—had declared that a state of war existed with Great Britain and the United States. That being so, there was no need to wait for the declaration by Congress. American time is very nearly six hours behind ours. The Cabinet, therefore, which met at 12.30 to-day, authorised an immediate declaration of war upon Japan. Instructions were sent to His Majesty’s Ambassador at Tokyo, and a communication was despatched to the Japanese Chargé de Affaires at 1 o’clock to-day to this effect: