The article defends the proposition that the distinctive diplomatic legacy of John Quincy Adams constitutes an important case study documenting the significance of moral reasoning in the statesman's obligation to uphold the national interest in a universal system of power politics. Recourse to political ethics afforded Adams a vantage point from which to evaluate the volatile problem of intervention—viewed in terms of the moral responsibilities and limits of American power—at a crucial turning point in the diplomatic history of the young republic. Important in this connection is how Adams attempted to reconcile the blessings of liberty with the methods and purposes of American diplomacy within and beyond the Western Hemisphere.An attempt is made to evaluate the sources and meaning of statesmanship for Adams who—as perhaps the nation's most experienced diplomat and accomplished Secretary of State—judged the limits and opportunities of American power from a perspective that considered moral precepts and international law as compatible with the prudent pursuit of American national interest in world affairs.