We are often told (by Barack Obama among others) that our ancestors sought a "more perfect union" in the creation of the United States. The implication is that they sought a worldly and more or less secular utopia. They did not. The contemporary meaning in those words from the constitution of the United States was that the framers sought a more efficient and effective government than that which had existed under the Articles of Confederation. The framers were solely concerned with the practicalities of government in their new country. The "more perfect union" phrase is one of a number of goals listed and is clearly not intended as the governing theme of the Constitution.
Having chosen to misunderstand the preamble to the constitution, and therefore the "purpose" of America, much of our ruling class now profess to believe that it is the purpose of the country to "reform" our society to their taste and to inflict the same norms on the rest of the world. To that end it is held to be more or less self-evident that ancient motivations for international policy are at an end and that all, all of mankind should re-organize itself to our taste.
In pursuit of that belief the United States in the 21st Century seeks revolutionary change everywhere and to accomplish that has been willing and continues to be willing to pay very high prices in blood and treasure even unto the risk of nuclear war with those with whom we can truly commit mutual suicide.