The Russo-Japanese war was an imperialistic conflict for the territory in Manchuria and Korea. The Russians were a strong imperial power that needed a warm water port on the Pacific Ocean, such as Port Arthur, that would be functional all year, but the Japanese weren't going fall out of Korea. Japan was a young country and although they had just defeated China in the First-Sino Japanese War they wanted to prove to the world that they were a power that needed to be reckoned with. Japan, who had the world betting against them, declared war against the ever confident Russia, who thought that with the defeat of Japan they would be able to stop the growing tension of Revolution back at home. The unexpected Japanese victory led the way for Japanese growth and recognition as a rising power and changed the balance of power in East Asia giving way to Japanese growth and leading to the Russian Revolution in 1905.
One of the main causes of the conflicts that occurred between Russia and Japan in the early 1900's was the Sino-Japanese War. Japan had emerged from the Meiji Restoration, and was expanding and growing adopting more of the Western train of thought. Through expansion and large scale industrialization Japan needed more places to expand and flourish as a country. Korea became a huge player in Japanese policy because Japan needed control over Korea in order to utilize its natural resources and to protect itself from future invasions. After the defeat of China in the First-Sino Japanese war the Treaty of Shimonoseki was signed by both the Empire of Japan and the Qing Empire of China leading to the Japanese control over the Liadon Peninsula which included the Port of Arthur.
After Japan gained control of Port Arthur, a warm water port in the Pacific that Russia needed to be successful in world trade and to build up a strong and centralized Navy. In order to prevent Japanese control of the Port, Russia looked toward their powerful friends, France and Germany, in order to try and get the Port of Arthur out of Japanese hands. Germany was compelled to help Russia in getting back the Liadong Peninsula because Germany wanted to implant its own sphere of influence in the East and because it wanted the Russians to focus on what was happening in the East rather than towards the West and Germany. France was bound to help the Russians because of the military alliance formed by both powers in 1892. With the help of these Western powers the Japanese government grudgingly agreed to take its forces out of the Liaodong Peninsula on 5 May 1985 for 450 million yen (around 5.02 million dollars). Mutsu's Kenkenroku suggests that Japans renouncement from the Port of Arthur was a "tactical move made without great hope of success."(Nish 27)
Russia was helped most by the Triple Intervention because it was slowly expanding into the East with the building of the Trans-Siberian railroad and having Port Arthur available would only allow them to increase diplomacy in the East. All Japanese forces had left the Liaodong Peninsula and Port Arthur by December 1895. By December 1897 Russia had already had a fleet occupying Port Arthur and began to make agreements with China to lease the Port. Soon after the Russians began to not only control the port, but began to build a railroad which led from Harbin through Mukden to Port Arthur. This railroad would expedite the transportation of Russian goods and exports to the Port which would help the Russian economy.
This railway was a contributor in the start of the Boxer Rebellion because of Russian influence in China and conflicts along the railways in Manchuria, Russia's main concern. With rising violence in North China and Beijing resulting from "Boxers" killing foreign missionaries, Chinese Christians, and civilians troops from eight different major countries to attempt to control and stop the violence. The most important member of the Eight-Nation Alliance, as it was called, that showed up to China was Russia. Russia, during this time when it was supposed to be stopping the Boxer Rebellion, sent its troops to Manchuria in order to solidify its control over Port Arthur. Japan began to mistrust Russia and its intentions in Manchuria. General Iguchi, a leader of the pro-war party in Japan, considered Russia to be "in a mood of expansion to west and east and south and expressed the opinion that she was devoting all her strength to expansion in Manchuria and Korea and should be resisted on both." (Nish 157)
As Japan began to negotiate with the Russian forces about their presence in Manchuria and Port Arthur tensions grew. By 6 February 1904 communication between the two nations had been cut off, and Japan, by that time, had already ordered five submarines from the United States and had allied with Britain in the Anglo-Japanese Alliance in 1902.
On 8 February 1904 is when Japan officially declared war with Russia, but the war actually started before Russia received the declaration from Japan. Three hours before Russia received the declaration the Japanese Imperial Navy, commanded by Admiral Heihachiro Togo, attacked the Russian fleet at Port Arthur. The following morning, and weeks following Togo and his ships continued to attack the Russian's with bombardments, and three night attempts to sink blockships in the harbor entrance in order to bottle up Russian ships. Although the Russians were unable to be driven out of the harbor these attacks at battle's allowed the Japanese to enter Korea through Incheon and three months later were able to cross into Manchuria.
The Japanese entrance into Manchuria was let by General Kuroki. By the beginning of April the Japanese reached the southern banks of the Yalu River at Wiju. On the opposite side of the river, ninety yards from the opposite bank, stood the Russian forces who, commanded by General Zasulich, were instructed to "meet the Japanese with 'firmness and prudence'" and to "fight a decisive action, given the Japanese numerical superiority." (Westwood 41) Russia remained on the defensive, so Kuroki and his troops knew that he needed to act. After making survey's of the Russian defense line Kuroki captured the midstream islands and used them as a point to cross the Yalu river six miles upstream where the Russian forces were weak. This first large scale land attack resulted in heavy losses for Japanese forces because of Russian trenches, but it did push the defensive Russian forces back towards Port Arthur.The Japanese government regarded Korea, which was geo-politically close to Japan