How, in the final analysis, can missionary diplomacy be explained? What were Wilson's motives and objectives? No single explanation will suffice, although there were unquestionably occasions when one consideration carried more weight than others. First, Wilson's concern about democracy and constitutionalism was genuine, and this was probably the main component of his Latin American policy when his administration began. What makes acceptance of this point difficult is that from the beginning, Wilson apparently assumed that the United States might have to use a heavy hand, to act undemocratically to install democracy. It was hard to see his commitment to constitutionalism in the midst of the bombardment of Veracruz or the U.S. marines' occupation of Santo Domingo, but it was there. Revolutions were unconstitutional and had to be prevented; illegitimate governments could not be recognized.
There is a second explanation for Wilson's policy that became clearer as World War I progressed—concern about the security of the hemisphere. Potential enemies, such as Germany, became of increasing concern. State Department documents illustrate the point clearly. What more startling example than the 1917 Zimmerman telegram, in which the German foreign minister invited Mexico to ally with Germany against the United States in the event of a German-American war? Security considerations were not always the primary explanation for missionary diplomacy, but they were constant concerns for Wilson, the State Department, and diplomats in the field. With a world war being fought during most of the Wilson presidency, and with the United States a belligerent by 1917, the situation was understandable.
There are also economic explanations for missionary diplomacy. As had long been the case, American entrepreneurs hoped to increase trade, find new markets and raw materials, and expand investment fields. Clearly these goals were applicable to Latin America during the Wilson administration. The available evidence does not prove conclusively that Wilson's central objective, as some scholars insist, was to advance U.S. economic interests. But facilitating the work of these interests, and giving them diplomatic protection, was important to Wilson and the State Department. Some diplomats, such as Henry Lane Wilson in Mexico and James Sullivan in the Dominican Republic, were dominated by their personal economic interests.
Missionary diplomacy contributed enormously to the Yankeephobia that had been building steadily in Latin America since the late nineteenth century. The task of the interwar presidents and the State Department was to dispel this aura of hostility. Considerable progress came with what came to be known as the Good Neighbor Policy, which reached its peak in the late 1930s. Whether the Good Neighbor Policy represented substantive change or merely a shift in rhetoric and tactics is debatable. Whatever the case, Woodrow Wilson, the practitioner of missionary diplomacy, made the Good Neighbor Policy, or something similar, a necessity.