In the words of Inoue Karou, the war was “divine aid…for the development of the destiny of Japan.” Why did the Japanese feel this way?
Japan had asserted itself on the world stage just a decade earlier during the Russo-Japanese War of 1904-1905. Japan unexpectedly won victory after victory in that conflict, ruining the Russians’ bid to expand to the Pacific. More impressively, however, were the nature of these victories: in the last two major battles of the war (The Battles of Mukden and Tsushima), the Russians lost over 90,000 troops and then 8 battleships and numerous smaller warships. Russia sued for peace, with Theodore Roosevelt helping to mediate the Treaty of Portsmouth.
Less than 10 years later, the Japanese saw an opportunity to put themselves on stage again, pursuing their interests in the far east while the major powers of Europe were embroiled in their own conflict. Thus, Japan pointed to its 1902 alliance agreement with Great Britain in an ultimatum directed towards Germany: “We consider it highly important and necessary in the present situation to take measures to remove the causes of all disturbance of peace in the Far East, and to safeguard general interest as contemplated in the Agreement of Alliance between Japan and Great Britain.”
Germany never did grace the Japanese with a reply.