Japan waged an undeclared war on China from July 7, 1937, and China resisted that undeclared war without technically announcing the existence of a state of war until December 9, 1941, when the text of the declaration was issued by Lin Sen, President of the Chinese Republic.
Japan's national policy has always aimed at the domination of Asia and mastery of the Pacific. For more than four years China has resolutely resisted Japan's aggression, regardless of suffering and sacrifice, in order not only to maintain her national independence and freedom but also to uphold international law and justice and to promote world peace and human happiness.
China is a peace-loving nation. In taking up arms in self-defense, China entertained the hope that Japan might yet realise the futility of her plans of conquest. Throughout the struggle all the other powers have shown the utmost forbearance likewise in the hope that Japan might one day repent and mend her ways in the interest of peace in the entire Pacific region.
Unfortunately Japan's aggressive capacities prove to be incorrigible. After her long and fruitless attempt to conquer China, Japan, far from showing any signs of penitence, has treacherously launched an attack on China's friends, the United States and Great Britain, thus extending the theater of her aggressive activities and making herself the arch-enemy of justice and world peace.
This latest act of aggression on the part of Japan lays bare her insatiable ambitions and has created a situation that no nation which believes in international good faith and human decency can tolerate.
The Chinese Government hereby formally declares war on Japan. The Chinese Government further declares that all treaties, conventions, agreements and contracts regarding relations between China and Japan are and remain null and void.
(The Chinese Government's Declaration of War on Germany and Italy.)
Since the conclusion of the Tripartite Pact of September 1940, Germany, Italy, and Japan have unmistakably banded themselves into a block of aggressor states working closely together to carry out their common program of world conquest and domination. To demonstrate their solidarity Germany and Italy successively accorded recognition to Japan's puppet regimes in northeastern China and at Nanking. As a consequence, China severed her diplomatic relations with Germany and Italy last July. Now the Axis powers have extended the theater of their aggressive activities and thrown the whole Pacific region into turmoil, making themselves the enemies of international justice and world civilization.
This state of affairs can no longer be tolerated by the Chinese Government and people. The Chinese Government hereby declares that as from midnight, December 9, 1941, a state of war exists between China and Germany and between China and Italy. The Chinese Government further declares that all treaties, conventions, agreements, and contracts regarding relations between China and Germany and between China and Italy are and remain null and void.
Sources: Contemporary China, Vol. 1, no. 15, December 15, 1941; ibiblio