Monroe put forth a proclamation in which he declared that America was no longer a field for European colonization, and that any attempt on the part of a European power to control the destiny of an American community would be taken as a sign of "an unfriendly disposition towards the United States."
Canning let it be understood that England backed the declaration, and that any attempt to extend the operations of the Holy Alliance to America would have to be carried out in the teeth of the combined opposition of the two great maritime powers so recently at war with each other. The plan was abandoned, and the independence of the South American Republics was successfully established.
But much more was established. The "Monroe Doctrine" became, and remains to-day, the corner-stone of American foreign policy. It has been greatly extended in scope, but no American Government has ever, for a moment, wavered in its support. None could afford to do so. To many Englishmen the doctrine itself, and still more the interpretation placed upon it by the United States in later times, seems arrogant--just as to many Americans the British postulate of unchallengeable supremacy at sea seems arrogant. But both claims, arrogant or no, are absolutely indispensable to the nation that puts them forward. If the American Republic were once to allow the principle that European Powers had the right, on any pretext whatever, to extend their borders on the American Continent, then that Republic would either have to perish or to become in all things a European Power, armed to the teeth, ever careful of the balance of power, perpetually seeking alliances and watching rivals. The best way to bring home to an honest but somewhat puzzled American--and there are many such--why we cannot for a moment tolerate what is called by some "the freedom of the seas," is to ask him whether he will give us in return the "freedom" of the American Continent. The answer in both cases is that sane nations do not normally, and with their eyes open, commit suicide.
During the "era of good feeling" in which the Virginian dynasty closed, forces had been growing in the shadow which in a few short years were to transform the Republic. The addition to these forces of a personality completed the transformation which, though it made little or no change in the laws, we may justly call a revolution.