 Following the attack on Pearl Harbor, the United States declared war against Japan, and within days China joined the Allies in formal declaration of war against Japan, Germany and Italy.As the Western Allies entered the war against Japan, the Sino-Japanese War would become part of a greater conflict, the Pacific theatre of World War II.Almost immediately, Chinese troops achieved another decisive victory in the Battle of Changsha, which earned the Chinese government much prestige from the Western Allies.