Answer:
In 1904, the Russian Empire, which was ruled by the autocratic Czar Nicholas II, was one of the largest territorial powers in the world.
However, with the Siberian shipping center of Vladivostok forced to close for much of the winter months, the empire was in need of a warm-water port in the Pacific Ocean, both for purposes of trade as well as a base for its growing navy.
Czar Nicholas set his sights on the Korean and Liaodong peninsulas, the latter located in present-day China. The Russian Empire already leased a port on the Liaodong Peninsula from China—Port Arthur—but it wanted to have a base of operations firmly under its control.
The Japanese, meanwhile, had been concerned about Russian influence in the region since the First Sino-Japanese War of 1895. Russia provided military support to the Qing Empire in China during that conflict, which pitted the two Asian powers against each other.
With the Russians’ history of military aggression, the Japanese initially sought a deal, offering to cede control of Manchuria (northeastern China). Under the terms of the proposal, Japan would have maintained influence over Korea.
However, Russia refused Japan’s offer and demanded that Korea north of the 39th parallel serve as a neutral zone.
As negotiations broke down, the Japanese opted to go to war, staging a surprise attack on the Russian navy at Port Arthur on February 8, 1904.