Another maxim of political action is that which has become known as the "Monroe Doctrine." While enunciated by a single state, it had in view the maintenance of the independence of the states of the American continent. For many years after the Revolutionary War the opinion prevailed that Europe viewed with disfavor the growth of the American republic. The Holy Alliance, formed on the downfall of Napoleon, was followed by several congresses of European powers, at one of which, held at Verona in 1822, the subject of helping Spain recover her revolting colonies in America was discussed. This led to the declaration of President Monroe in his message of Dec. 2, 1823, that there should be, (1) no more European colonies on these continents, (2) no extension of the European political system to any portion of this hemisphere, (3) no European interposition in the affairs of the Spanish-American republics. This doctrine has been repeatedly affirmed by the United States, and in some instances very liberally interpreted. It in no way embodies a principle of international law, though the European and other states may regard it as expressing the attitude of the United States upon the points covered, and if desirous of avoiding friction, govern themselves accordingly. If it were a principle of international law, the United States would not be justified in changing its attitude upon the doctrine, but probably it would not be seriously maintained that the United States might not enunciate another policy setting aside the Monroe Doctrine. Reddaway well says, "that it produced its desired effect as an act of policy, but in no way modified the Law of Nations."[100] This doctrine cannot be considered as outlining a principle of non-intervention, as has sometimes been claimed, but it rather announces a policy of intervention on the part of the United States to anticipate intervention by other powers.
The doctrine has always failed of legislative indorsement, and has been strenuously opposed by European powers. That it has been recognized, however, to a certain extent, appears by the course of events.[101] It was recently applied in the case of the intervention by the United States in the dispute over the boundary between Venezuela and British Guiana. Great Britain and the United States settled the difficulty by a submission to arbitration.[102]