U.S. President Theodore Roosevelt sought to prevent European intervention, largely to protect the routes to the future Panama Canal, as the canal was already under construction. He made a small military intervention to ward off the European powers, proclaimed his famous Roosevelt Corollary to the Monroe Doctrine, and in 1905 obtained Dominican agreement for U.S. administration of Dominican customs, then the chief source of income for the Dominican government. A 1906 agreement provided for the arrangement to last 50 years. The United States agreed to use part of the customs proceeds to reduce the immense foreign debt of the Dominican Republic, and assumed responsibility for said debt.[41][17]
After six years in power, President Ramón Cáceres (who had himself assassinated Heureaux)[38] was assassinated in 1911. The result was several years of great political instability and civil war. U.S. mediation by the William Howard Taft and Woodrow Wilson administrations achieved only a short respite each time. A political deadlock in 1914 was broken after an ultimatum by Wilson telling Dominicans to choose a president or see the U.S. impose one. A provisional president was chosen, and later the same year relatively free elections put former president (1899–1902) Juan Isidro Jimenes Pereyra back in power. In order to achieve a more broadly supported government, Jimenes named opposition individuals to his Cabinet. But this brought no peace and, with his former Secretary of War Desiderio Arias maneuvering to depose him and despite a U.S. offer of military aid against Arias, Jimenes resigned on May 7, 1916.[42]
The 1916 occupation by U.S. Marines
Wilson thus ordered the U.S. occupation of the Dominican Republic. U.S. Marines landed on May 16, 1916, and had control of the country two months later. The military government established by the U.S., led by Rear Admiral Harry Shepard Knapp, was widely repudiated by Dominicans. Some Cabinet posts had to be filled by U.S. naval officers, as Dominicans refused to serve in the administration. Press and radio censorship was imposed, as were limits on public speech. Guerrilla war against the U.S. forces was met with a vigorous, "often brutal" response.[42]
But the occupation regime, which kept most Dominican laws and institutions, had its positive effects. It largely pacified the country, revived the economy, reduced the Dominican debt, built a road network that at last connected all regions of the country, and created a professional National Guard to replace the warring partisan units.[42]
Opposition to the occupation continued, however, and after World War I it increased in the U.S. as well. There, President Warren G. Harding (1921–23), Wilson's successor, worked to end the occupation, as he had promised to do during his campaign. U.S. government ended in October 1922, and elections were held in March 1924.[42]
The victor was former president (1902–03) Horacio Vásquez Lajara, who had cooperated with the U.S. He was inaugurated on July 13, and the last U.S. forces left in September. Vásquez gave the country six years of good government, in which political and civil rights were respected and the economy grew strongly, in a peaceful atmosphere.