Which war did President Theodore Roosevelt help negotiate to prevent one nation from dominating trade in China?

The correct answer is the war between Japan and Russia. President Theodore Roosevelt played a crucial role in negotiating the Treaty of Portsmouth, which ended the Russo-Japanese War in 1905. This conflict arose over ambitions in East Asia, particularly concerning Korea and parts of China, including the vital trade avenues being established.

Roosevelt's involvement was driven by concerns about maintaining a balance of power in the region, particularly to prevent Japan from gaining complete dominance over China. He was motivated to facilitate peace talks to ensure that no single nation would threaten open trade policies or assert uncontested control over Chinese markets, which were of significant interest to the United States and other Western powers.

His successful mediation earned him the Nobel Peace Prize in 1906, marking the first time an American president received this honor for diplomatic efforts. The significance of this negotiation lies not only in the immediate cessation of hostilities but also in Roosevelt's broader vision of promoting stability and open trade in Asia, thus reinforcing America’s position as a world power interested in maintaining equilibrium against imperial ambitions.