Russia at the time of the Boxer Rebellion of 1900 suffered significant losses in areas along the Chinese Eastern Railway in Manchuria. However, they built towns, such as Harbin, along the railway and extended the line southward after obtaining a lease of Port Arthur and Talienwan. They even developed coal mines. Since a significant amount of investment was made, they believed they worried about their protection. Therefore, large armed forces were sent and Russia de facto occupied Manchuria.
Britain, which was expanding her interests along the Yangtze River, regarded Russian occupation of Manchuria as a potential threat to British interests. Japan, which had been prevented from occupying the Liaotung Peninsula by the Tripartite Intervention, felt uncomfortable when the Russians leased the peninsula from China. In addition, there was the Russian occupation of Manchuria. Japan, together with the United States and Britain, was keen to expel Russian soldiers from Manchuria. In 1901 in the light of such circumstances, a German diplomat in London proposed a triple alliance in the Far East of Japan, Britain and Germany. The German proposal was not realized, but Japan took this opportunity to initiate separate negotiations with Britain. Britain, which had suffered from the Boer War and was unable to prevent Russian expansion in the Far East, thought of using Japan as a barrier against Russia. With both interests coinciding, the negotiations received increased momentum from November 1901, and the Anglo-Japanese Alliance was signed in London on 30 January 1902.
Under the first Anglo-Japanese Alliance, it was made compulsory for the contracting parties to observe the following: (a) if either Great Britain or Japan should become involved in war with another Power, the other High Contracting Party will maintain a strict neutrality, and use its efforts to prevent other Powers from joining in hostilities against its Ally; (b) if, in the above event, any other Power or Powers should join in hostilities against the Ally, the other High Contracting Party will come to its assistance and will conduct the war in common, and make peace in mutual agreement with it. In addition, Japan made Britain agree that Japan had in a peculiar degree