In the wake of the Spanish‐American War, the United States joined the ranks of the imperial powers with possessions that stretched halfway around the globe, from Puerto Rico in the Caribbean to the Philippines in the Pacific. In the years leading up to its entry into World War I, America did its best to maintain its influence in Asia through diplomacy while following an aggressive foreign policy in the Western Hemisphere. The United States showed little interest in European affairs until the outbreak of war in August 1914 and even then remained officially neutral for almost three years. The commitment of American troops in 1917 was a significant factor in the Allied victory and earned President Wilson the right to help shape the peace settlement. The failure of the Senate to ratify the Treaty of Versailles, however, marked a shift toward a more isolationist foreign policy.
As a two‐ocean conflict, the Spanish‐American War underscored the value of a canal linking the Atlantic and Pacific Oceans. The French had tried but failed to construct a canal across the Isthmus of Panama in the 1880s, so the United States decided to take over the project. Under the Hay‐Herran Treaty (1903), Columbia agreed to a 99‐year lease of a six‐mile‐wide strip of land in Panama (a province of Columbia at the time) in return for a $10 million cash payment and an annual fee of $250,000. When the Columbian Senate refused to ratify the treaty, the Panamanians mounted a successful revolt that had the tacit approval of the Roosevelt Administration. Sending warships to prevent Columbia from taking action, the United States quickly recognized Panama's independence. A new agreement — the Hay‐Bunau‐Varilla Treaty — gave the United States full control and sovereignty over the Canal Zone (an area ten miles wide across the isthmus) in return for the same financial arrangements made with Columbia. Construction on the Panama Canal began in 1904, and the first ship passed through the locks in 1914. While the canal construction was a major feat of engineering, medical advances that occurred during the ten‐year period, such as the eradication of yellow fever and better control over malaria and other tropical diseases were important accomplishments as well.
American intervention in the Caribbean and Central America. Throughout the Progressive Era and well into the 1920s, the United States followed a policy of intervention in the Caribbean and Central America. Under the Platt Amendment (1901), which was incorporated into the Cuban constitution and a Cuban‐American treaty, the United States could intervene to preserve the independence or political and social stability of Cuba. Furthermore, Cuba agreed to grant land for an American naval base on the island (Guantanamo Bay), not to sign a treaty with another country that impaired Cuba's sovereignty, and not to incur a debt that could not be repaid out of current revenues. The U.S. government used this amendment as the justification for sending American troops into Cuba in 1906, 1912, and 1917.
Similarly, the Roosevelt Corollary to the Monroe Doctrine (1904) maintained that “chronic wrongdoing” by any nation in the Western Hemisphere might force the United States to exercise its “international police power”; that is, it would intervene. Under this principle, the finances of the Dominican Republic came under American control through a treaty, and after a revolution threatened these arrangements in 1916, U.S. troops occupied the country for the next eight years. Essentially the same policy was applied to Haiti, where American civilian personnel and military forces remained on the island from 1915 to 1934. When a revolt against the government jeopardized American interests in Nicaragua in 1912, U.S. Marines arrived and stayed until 1925. They were back a year later to put down another round of civil unrest. As a possible site for a second interocean canal, Nicaragua was particularly important, and the United States wanted to make sure no foreign power gained control of the route.
U.S. policy in Asia. At the turn of the century, Japan was the major power in Asia. Fearful of Japanese dominance, Roosevelt played peacemaker in the conflict that broke out between Japan and Russia in 1904 in the hope of limiting Japanese gains. The Treaty of Portsmouth (1905), which ended the Russo‐Japanese War and earned the president the Nobel Peace Prize, recognized Japan's influence in Manchuria (a province of China) but did not include a cash indemnity and required Russia to give up only half of Sakhalin Island. At the same time, in the Taft‐Katsura Agreement (1905), the United States and Japan acknowledged the United States' control of the Philippines and Japan's control of Korea. Despite the tensions that arose because of immigration and the Gentlemen's Agreement, relations between the two countries remained good. They agreed to respect the territorial integrity of each other's possessions in Asia, and Japan reconfirmed its support for the Open Door Policy through the Root‐Takahira Agreement (1908).
Taft's foreign policy relied on dollar diplomacy — spreading American influence through the economic penetration of overseas markets by U.S. corporations. In an attempt to maintain the independence of China, the administration unsuccessfully tried to establish an international banking syndicate that would buy back the railroads in Manchuria that were in the hands of the Japanese. The combination of a Japanese‐Russian alliance and a lack of support from the Wilson administration led U.S. investors to reject the project. On the whole, dollar diplomacy was more effective in Central and South America than it was in Asia.
Relations with Mexico. Opposing the regime of General Victoriano Huerta, who had come to power in Mexico following the May 1911 revolt, the Wilson administration supported the revolutionary movement headed by Venustiano Carranza. American troops attacked Veracruz in April 1914, which ultimately led to Huerta leaving office and Carranza and his supporters occupying Mexico City. These developments were soon marred by infighting between Carranza and one of his generals, Pancho Villa. When Villa's forces raided a town in New Mexico in 1916, Wilson ordered the U.S. Army to mount a punitive expedition into Mexico to capture him. This prolonged intrusion brought the United States and Mexico to the brink of war until the troops were withdrawn in January 1917.