Answer:
The Russo-Japanese War, from February 8, 1904 to September 5, 1905, was a conflict arising from the rival imperialist ambitions of the Russian Empire and the Empire of Japan in Manchuria and Korea. The main scenarios of the conflict were the area around the Liaodong peninsula and Mukden, the seas of Korea and Japan and the Yellow Sea.
The Russians were looking for a port of warm waters (which would not freeze in winter) in the Pacific Ocean for use by their Navy and for maritime trade. The port of Vladivostok could only operate during the summer, but Port Arthur (China) would be able to keep running all year round.
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The war grew out of rival ambitions of the Russian Empire and the Empire of Japan. Both of them sought control over Manchuria and Korea.
The war started when Japan offered to recognize Russian dominance in Manchuria in exchange for recognition of Korea as a Japanese sphere of influence. Russia refused, and demanded that Korea north of the 39th parallel be a neutral buffer zone between the two powers. The Japanese government perceived this as a direct threat to its strategic interests from the Russian Empire, and chose to go to war.