In the second half of the 19th century, the emerging imperial powers, Japan and Russia, vied in seizing territory from an enfeebled China. By the Treaty of Aigun (1858) Russia annexed Amur; the Treaty of Tientsin (1860) conferred Ussurri. The Sino-Japanese war (1894–95) gave Japan sway over Korea, but Russia muscled in to seize Port Arthur, a key warm water port, and occupied Manchuria after the Boxer rebellion. When Russia failed to implement an agreed withdrawal from Manchuria, Japan attempted a diplomatic solution but, rebuffed, declared war in February 1904. Japan inflicted a series of crushing defats on Russia, culminating in the Battle of Mukden and the sea Battle of Tsushima. Russia was forced to sue for peace. The Treaty of Portsmouth, signed under US auspices, specified the Russian vacation of Manchuria, but allowed them a lease on Port Arthur, while Japan’s annexation of Korea was ratified.
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