I was looking at Treyarchs twitter and their header looked like a hint to me

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I looked up a war between Russia and japan and found this out,

The Russo-Japanese War (8 February 1904 5 September 1905) was "the first great war of the 20th century."[4] It grew out of rival imperial ambitions of the Russian Empire and the Empire of Japan over Manchuria and Korea. The major theatres of operations were Southern Manchuria, specifically the area around the Liaodong Peninsula and Mukden; and the seas around Korea, Japan, and the Yellow Sea.

Russia sought a warm water port[5] on the Pacific Ocean, for their navy as well as for maritime trade. Vladivostok was only operational during the summer season, but Port Arthur would be operational all year. From the end of the First Sino-Japanese War and 1903, negotiations between Russia and Japan had proved impractical. Japan offered to recognize Russian dominance in Manchuria in exchange for recognition of Korea as a Japanese sphere of influence. Russia refused this, so Japan chose war to counter the Russian aggression in Asia. After discussions broke down in 1904, the Japanese Navy attacked the Russian eastern fleet at Port Arthur, a naval base in the Liaotung province leased to Russia by China, which led to war. The Japanese defeated the Russians in a series of battles on land and at sea.

The resulting campaigns, in which the Japanese military attained victory over the Russian forces arrayed against them, were unexpected by world observers. Over time, the consequences of these battles would transform the balance of power in East Asia, resulting in a reassessment of Japan's recent entry onto the world stage.