On St George's Day 1895 the "triple intervention" of Russia, Germany and France caused the renegotiation of the Treaty of Shimonoseki and thereby, in my opinion, set the stage for the subsequent Russo-Japanese war as well as the seeds of the Japanese nationalism that led inexorably to Japan's involvement in World War II.
The Treaty of Shimonoseki was the peace treaty of the Sino-Japanese war, where the Japanese comprehensively defeated China over the question of who would control Korea. The treaty gave Japan control of Korea, Taiwan and the Liaodong Peninsula in Manchuria. However the European powers were unwilling to see Japan get so much additional territory and the triple intervention forced the Liaodong Peninsular to be handed back in exchange for money. Just three years later Russia occupied the peninsular rubbing in the fact that the Europeans considered Japan to be a second class nation (FWIW China was a third class nation, just one step up from being a colony). A gentleman by the name of Bill Gordon has written a number of interesting essays on Japan including a couple on the Meiji period and imperialism. From the latter:
The theory of nationalism provides the best explanations for Japan's imperialistic actions between 1894 and 1905. The following points support nationalism as the best theory to understand Japan's wars and colonial acquisitions: (1) Japan's deep concerns for national security, (2) its emulation of the imperialistic behaviors of Western powers, and (3) Japanese national ideals and personal characteristics.
The United States forcibly opened Japan to the outside world in 1853. Soon thereafter, Japan was pressured by the imperialist powers to sign "unequal treaties," which granted foreigners in Japan extraterritoriality in legal cases and which imposed on Japan low tariff rates for which the imperialist countries did not grant corresponding concessions in their rates. The leaders of the Meiji government, formed in 1868 after the downfall of the Tokugawa Shogunate, considered national security and defense to be the top priority in order to prevent subjugation by the Western powers. The nationalistic policy of fukoku kyomacr;hei (rich country, strong military) emphasized Japan's goals to develop the country economically to catch up with the Western powers and to increase its military strength to ensure its existence as an independent country. Japan fought the later wars against China and Russia in 1894-5 and 1904-5, respectively, to ensure that Korea would not be used by another imperialist power to threaten Japan's security.
Japan emulated the imperialistic behaviors of the Western powers. From the beginning of the Meiji Period in 1868, Japan's leaders sought to make the country an industrial and military power on par with the Western imperialist powers. When Japan emerged from its isolation and took steps to industrialize and modernize, the international environment was one of intense competition between powers that tried to maximize their political and economic positions relative to other powers and less developed countries. Overseas colonies provided the imperialist powers with prestige and status, so Japan's leaders naturally celebrated when its empire expanded to include Taiwan, Korea, and the Kwantung Leased Territories.
It is hard to blame Japan for feeling threatened in the late 19th century, and indeed it is to its credit that it recognised the threat of foreign domination and reacted constructively to it. The problem is that the European powers taught it the wrong lessons in their actions and reactions. In my opinion the triple intervention was the the worst lesson because it taught Japan's leaders two lessons. The first was that the only way it could keep its gains (and indeed its security) was to be independantly strong militarily which gave great impluse to an already traditionally military society to continue on that path. The second was that Asians were less important that Whites in the grand scheme of things. The fact that two Asian powers had concluded a treaty in good faith was nothing unless the white man approved. If he didn't then the treaty had to be modified until he did.
Had the triple intervention not taken place then perhaps Japan would have become more mercantilist and less military, folliwing the British Empire's example rather than that of the Russian or Prussian. The fact that it went the other way has reverberated down to today and the current tensions between China and Japan.