Historically, Japan's main foreign preoccupation has been China. The Korean Peninsula, a strategically located feature critical to the defense of the Japanese archipelago, greatly occupied Japan's attention in the nineteenth century. Earlier tension over Korea had been settled temporarily through the Treaty of Kanghwa in 1876, which opened Korean ports to Japan, and through the Tianjin Convention in 1885, which provided for the removal from Korea of both Chinese and Japanese troops sent to support contending factions in the Korean court. In effect, the convention had made Korea a co-protectorate of Beijing and Tokyo at a time when Russian, British, and United States interests in the peninsula also were on the increase. A crisis was precipitated in 1894 when a leading pro-Japanese Korean political figure was assassinated in Shanghai with Chinese complicity. Prowar elements in Japan called for a punitive expedition, which the cabinet resisted. With assistance from several Japanese nationalistic societies, the illegal Tonghak (Eastern Learning) nationalistic religious movement in Korea staged a rebellion that was crushed by Chinese troops. Japan responded with force and quickly defeated China in the First Sino-Japanese War (1894-95). After nine months of fighting, a cease-fire was called and peace talks were held. The victor's demands were such that a Japanese protectorate over China seemed in the offing, but an assassination attempt on Li Hongzhang, China's envoy to the peace talks, embarrassed Japan, which then quickly agreed to an armistice. The Treaty of Shimonoseki accomplished several things: recognition of Korean independence; cessation of Korean tribute to China; a 200 million tael (Chinese ounces of silver, the equivalent in 1895 of US$150 million) indemnity to Korea from China; cession of Taiwan, the Penghu Islands, and the Liaodong Peninsula (the southern part of Manchuria) to Japan; and opening of Chang Jiang (Yangtze River) ports to Japanese trade. It also assured Japanese rights to engage in industrial enterprises in China.

Having their own imperialist designs on China and fearing China's impending disintegration, Russia, Germany, and France jointly objected to Japanese control of Liaodong. Threatened with a tripartite naval maneuver in Korean waters, Japan decided to give back Liaodong in return for a larger indemnity from China. Russia moved to fill the void by securing from China a twenty-five-year lease of Dalian (Dairen in Japanese, also known as Port Arthur) and rights to the South Manchurian Railway Company, a semioffical Japanese company, to construct a railroad. Russia also wanted to lease more Manchurian territory, and, although Japan was loath to confront Russia over this issue, it did move to use Korea as a bargaining point: Japan would recognize Russian leaseholds in southern Manchuria if Russia would leave Korean affairs to Japan. The Russians only agreed not to impede the work of Japanese advisers in Korea, but Japan was able to use diplomatic initiatives to keep Russia from leasing Korean territory in 1899. At the same time, Japan was able to wrest a concession from China that the coastal areas of Fujian Province, across the strait from Taiwan, were within Japan's sphere of influence and could not be leased to other powers. In 1900 Japanese forces participated in suppressing the Boxer Uprising, exacting still more indemnity from China.

Japan then succeeded in attracting a Western ally to its cause. Japan and Britain, both of whom wanted to keep Russia out of Manchuria, signed the Treaty of Alliance in 1902, which was in effect until in 1921 when the two signed the Four Power Treaty on Insular Possessions, which took effect in 1923 (see Diplomacy , this ch.). The British recognized Japanese interests in Korea and assured Japan they would remain neutral in case of a Russo-Japanese war but would become more actively involved if another power (probably an allusion to France) entered the war as a Russian ally. In the face of this joint threat, Russia became more conciliatory toward Japan and agreed to withdraw its troops from Manchuria in 1903. The new balance of power in Korea favored Japan and allowed Britain to concentrate its interests elsewhere in Asia. Hence, Tokyo moved to gain influence over Korean banks, opened its own financial institutions in Korea, and began constructing railroads and obstructing Russian and French undertakings on the peninsula.

When Russia failed to withdraw its troops from Manchuria by an appointed date, Japan issued a protest. Russia replied that it would agree to a partition of Korea at the thirty-ninth parallel, with a Japanese sphere to the south and a neutral zone to the north. But Manchuria was to be outside Japan's sphere, and Russia would not guarantee the evacuation of its troops. Despite the urging of caution by most genro, Japan's hardliners issued an ultimatum to Russia, which showed no signs of further compromise. War broke out in February 1904 with Japanese surprise attacks on Russian warships at Dalian and Chemulpo (in Korea, now called Inch'on). Despite tremendous loss of life on both sides, the Japanese won a series of land battles and then decisively defeated Russia's Baltic Sea Fleet (renamed the Second Pacific Squadron) at the Battle of Tsushima in May 1905. At an American-mediated peace conference in Portsmouth, New Hampshire, Russia acknowledged Japan's paramount interests in Korea and agreed to avoid "military measures" in Manchuria and Korea. Both sides agreed to evacuate Manchuria, except for the Guandong Territory (a leasehold on the Liaodong Peninsula) and restore the occupied areas to China. Russia transferred its lease on Dalian and adjacent territories and railroads to Japan, ceded the southern half of Sakhalin to Japan, and granted Japan fishing rights in the Sea of Okhotsk and the Bering Sea.

Japanese nationalism intensified after the Russo-Japanese War, and a new phase of continental expansion began after 1905. Politically and economically, Korea became a protectorate of Japan and in 1910 was formally annexed as a part of the empire. By means of the South Manchurian Railway, Japanese entrepreneurs vigorously exploited Manchuria. By 1907 Russia had entered into a treaty arrangement with Japan whereby both sides recognized the other's sphere of influence in Manchuria.

Data as of January 1994