For a long while after the gunfire has died away in the Dominican Republic, diplomats, lawyers, politicians and professors will be arguing the legality and morality of the U.S. intervention.
The U.S., of course, did not invent intervention—it has been an instrument of nations ever since there have been any. The U.S. has probably used that instrument with greater restraint, and less for the purpose of territorial aggrandizement, than any other major power in human history. Yet upon no fewer than 148 occasions—the latest being in the Dominican Republic—the U.S. has "intervened" in the sense of landing armed troops on foreign shores in situations short of declared war.
The classic use of U.S. military intervention, has been to enforce respect for American lives and property. Thus, in 1801, marines landed in Tripoli to free the crew of a seized U.S. ship. In 1849, a U.S. naval force debarked in Turkey to gain the release of an imprisoned American. In 1851, U.S. troops intervened on Johanna Island, off East Africa, to exact redress for the imprisonment of an American whaling captain.
A Bulwark Against Designs. But far more important than the protection of American nationals was worry that European countries might come over the Atlantic again to intervene in pursuit of old colonialist designs. This fear, in turn, gave rise to the U.S.'s enduring defensive bulwark against foreign encroachment in the Western Hemisphere: the Monroe Doctrine.
Contained in President James Monroe's State of the Union message on Dec. 2, 1823, the doctrine declared: "The occasion has been judged proper for asserting, as a principle in which the rights and interests of the United States are involved, that the American continents, by the free and independent condition which they have assumed and maintain, are henceforth not to be considered as subjects for future colonization by any European powers." Implicit in the Monroe Doctrine was the threat that the U.S. would oppose any such European intervention with armed force.
While the U.S. was occupied with the Civil War, Spain regained control of its former colony of Santo Domingo and France set up the Austrian Archduke Maximilian as Emperor of Mexico. But in 1865, shortly after Appomattox, the Spaniards cleared out of Santo Domingo; a year later France, under U.S. pressure, began pulling its troops out of Mexico, leaving Maximilian to die before a Mexican firing squad. In 1903, after Germany, Britain and Italy decreed a blockade of Venezuela to force the dictator of the day to pay claims due their citizens, President Theodore Roosevelt warned the Europeans away with a threat of intervention by the U.S. fleet.