As you are American, you probably have a better insight into American national psychology than I do. Nonetheless, I'll hazard a speculation.

The US seemed to be somewhat content to be left alone to its own devices until the tail end of the First World War when Wilson called for the "war to end all wars." The last vestiges of American isolationism went away after the end of the Second World War.

My take is that the US - or, at least, the foreign policy elite - is afraid of the rest of the world. It does not feel secure with itself unless everyone else gives it wide berth. Why this is the case, I don't know, maybe it was Empire of Japan's attack on Pearl Harbor that freaked America out permanently.

Which is why Hugo Chavez in Venezuela or, more dramatically, Soviet missiles in Cuba, are seen as existential threats that must be stamped out at all costs. And why dramatic images like the spectre of Communism, or radical Islam, are often used to justify expensive interventions, as if the rest of the world would "fall like dominos" under the sway of these ghosts unless America holds them back.

Thus, the way I understand it, the American foreign policy elite will permit regional powers like the EU, the African Union, India, and China to expand as long as they stay within their spheres of influence.

This, I feel, is how the State Department and the DOD see it. How the American public see it, I suspect, is quite different, but the degree to which the public can directly affect State Department and DOD policy is unclear to me.

Elections are well and good, but even changing Congress and the President every five years will likely do little because every elected official will need to rely on the unelected permanent bureaucracy to craft and execute policy. In this sense, I agree with Donald Trump's lament about the existence of a "deep state", but see this as largely an unavoidable consequence of developing the sort of bureaucracy necessary to manage a country of 330 million.