In Venezuela and Central America the situation was the reverse. During the war the State Department endorsed all-American oil concessions, but, in accordance with the principle of reciprocity, Hughes instructed his Latin-American ambassadors in 1921 to respect foreign interests. Latin America in general became far more of an American sphere of influence during the war than ever before owing to the growth of American commerce at Britain’s expense. Central American governments now relied on New York banks to manage their public finance rather than those of London and Paris, while the U.S. share of Latin-American trade totaled 32 percent, double Britain’s share, though British capital still predominated in the economics of Argentina, Brazil, and Chile.

Ever since the 17 republics of mainland Latin America emerged from the wreck of the Spanish Empire in the early 19th century, North Americans had viewed them with a mixture of condescension and contempt that focused on their alien culture, racial mix, unstable politics, and moribund economies. The Western Hemisphere seemed a natural sphere of U.S. influence, and this view had been institutionalized in the Monroe Doctrine of 1823 warning European states that any attempt to “extend their system” to the Americas would be viewed as evidence of an unfriendly disposition toward the United States itself. On the one hand, the doctrine seemed to underscore republican familiarity, as suggested by references to “our sister republics,” “our good neighbors,” our “southern brethren.” On the other hand, the United States later used the doctrine to justify paternalism and intervention. This posed a quandary for the Latin Americans, since a United States strong enough to protect them from Europe was also strong enough to pose a threat itself. When Secretary of State James G. Blaine hosted the first Pan-American Conference in 1889, Argentina proposed the Calvo Doctrine asking all parties to renounce special privileges in other states. The United States refused.

After the Spanish–American War in 1898 the United States strengthened its power in the Caribbean by annexing Puerto Rico, declaring Cuba a virtual protectorate in the Platt Amendment (1901), and manipulating Colombia into granting independence to Panama (1904), which in turn invited the United States to build and control the Panama Canal. In the Roosevelt Corollary (1904) to the Monroe Doctrine the United States assumed “an international police power” in cases where Latin-American insolvency might lead to European intervention. Such “dollar diplomacy” was used to justify—and probably made inevitable—the later “gunboat diplomacy” of U.S. military intervention in Santo Domingo, Nicaragua, and Haiti. In his first term President Wilson also became embroiled in the Mexican Revolution. An affront to U.S. sailors led to his bombardment of Veracruz (1914), and border raids by Pancho Villa prompted a U.S. expedition into northern Mexico (1916). The Mexican Constitution of 1917 then granted to the state all subsoil resources to prevent their exploitation by U.S. firms. Such revolutionary efforts to nationalize resources, however, only meant that they went undeveloped or were exploited at home by corrupt officials, while the United States retaliated by cutting off loans and trade. The Latin-American dilemma of weakness and disunity in proximity to a mighty and united power was thus insoluble through unilateral efforts or a Pan-American movement dominated by Washington.

Wilson’s proposed League of Nations seemed to offer Latin America a means of circumventing U.S. influence. But the United States inserted Article 21 to the effect that “Nothing in this Covenant shall be deemed to affect the validity of international engagements, such as treaties of arbitration or regional understandings like the Monroe Doctrine.” Secretary of State Hughes later defended U.S. behaviour by candidly questioning the ability of some Latin-American states to maintain public order, sound finance, and the rule of law. When the Chaco dispute between Bolivia and Paraguay erupted into war, League of Nations President Briand offered his personal good offices, but he refused to assert League authority for fear of irritating the United States. In the end, the Pan-American Commission of Inquiry assumed jurisdiction.

Latin-American protests grew in volume, especially in 1926, when a Mexican-supported leftist rebellion in Nicaragua prompted U.S. Secretary of State Frank B. Kellogg to report to the Senate Foreign Relations Committee on “Bolshevist Aims and Policies in Mexico and Latin America.” But intervention by United States marines in Nicaragua only paved the way for the dictatorial regime of the Somozas. At the Pan-American Conference of 1928, rivalry between Argentina and Brazil and the Chaco contestants, and the caution of other states, precluded their presenting a united Latin-American front. But the U.S. administrations of the decade did labour to improve the American image. The Clark Amendment of 1928 repudiated the Roosevelt Corollary, while Hoover toured 10 Latin-American nations after his election as president and repudiated the “big brother” role. In the 1920s, therefore, the United States continued to squeeze out European influence in Latin America but was itself moving slowly toward the “Good Neighbor” policy of the 1930s.