The author discusses the mediation mission of the US President T. Roosevelt, who made a significant contribution to the end of the bloody Russian-Japanese war of 1904-1905. Having offered assistance to the conflicting parties in search of a mutual compromise, he sought to use the contradictions between the great powers through skillful maneuvering in the interests of the increased influence of his own country on world politics. In the theory of the "balance of power" formulated by him, the main attention is paid to the distribution of control zones between major geopolitical players, while a significant place in international relations was given to the United States, which at the turn of the XIX-XX centuries actively joined the struggle for sales markets. When considering the "good deeds" of the President, the main emphasis is placed on the analysis of the various diplomatic means used by him to achieve his goals. He was one of the first to resort to the so-called "multilateral" diplomacy, which involved the complex application of both conventional and non-traditional measures of mediation. By assuming the role of an intermediary, he was able not only to achieve the delimitation of spheres of influence with Japan in East Asia, but also to "open the doors" for American capital to Northern China on the basis of the principle of the most favored nation. The Portsmouth Peace led to a change in the balance of power in the Asia-Pacific region, in which the United States, thanks to the successful mediation of Roosevelt, became the main player in international diplomacy. .