On the 8th December 1941, the US and UK declared war upon the Empire of Japan. The leaders who signed these declaration where Franklin D. Roosevelt of the USA and Winston Churchill of the UK.
The two Allies(UK and USA) declared war on Japan after the surprise attack on Pearl Harbour on the 7th December 1941. Roosevelt's declaration of war officially joined the USA into World War 2. It was on this day as well that Roosevelt gave his famous infamy speech.
Surprisingly the UK was the first country to declare war on Japan after the Japanese had attacked the UK terrotories of Hong Kong, Singapore and Malaya. Once both countries had declared war on Japan this begun the truly global conflict of WW2. Which was to end after the war in Europe on 2nd September 1945.
The war in the pacific is also infamous for ending with the only two atomic bombs ever used dropped on Japan.
