The US has a strong sense of isolationism -- hence the late entry to WWI and the abandoning of the League of Nations
Think of the preceding superpower -- Britain. If any small, non-European defied them, they sent in a gun-ship.
If the US acted uppity in the early 1800s, the British burned down Washington DC (as they did in 1812), if Zanzibar defied them, they bombarded it for 45 minutes until they surrendered
For Western European nations, this was too close to home, so the English played diplomatic tricks, dividing one against the other, chessboards
The English were feared and placated as they played their cards thinking of their country first.
The US is like a modern-day Athens, but with more "morals" in the sense that it has always debated if it is right to go and attack someone, even if that is in the US' interest
Imagine if the USA became utterly isolationist after WWII and shut itself up in North America. Then the USSR would carte-blanche walk over much of the world and it would have been incredibly cruel -- if you want to know cruel, meet someone from the Ukraine or Moldavia, I have
in the USSR, Stalin shifted nations from one place to another, the soviets destroyed ancient works of art and architecture, they destroyed peoples etc.
The US has not been "feared" in that way by its friends or even by the ambiguous (India in the late 60s and 70s comes to mind) but feared by its enemies -- the USSR never dared to directly challenge the USA after the Cuban missile crisis and China plays it's Sun-Tzu games carefully.
For a long time people have wished for the USA to decline. Now that that IS what is happening, we see the powerplay coming to effect
I see China as biding its time as the US declines -- no war against the US, but a carve-up of various parts -- South-East Asia and Africa comes to mind (unfortunately AC, I don't see a strong native African coalition as being able to oppose the Chinese colonisation).
India may be able to oppose the rise of the chicoms, but it still hasn't got its act together -- either internally or externally. It has made strides internally economically and militarily, but it has a long way to go AND is hampered by the cancer that is Pakistan. Externally, the Indians are silently creating a necklace of alliances from Japan to S. Korea to Singapore to Australia to the Philippines to oppose China, but this still has a way to go.
Europe as a whole is declining economically and will not be so relevant in the future
South America I see as being dominated by Brazil and some kind of Spanish coalition of Chile-Colombia-Argentina with the other mixed states as being by the wayside.
Even if the US could dominate the World militarily and economically in the past, it can no longer do so now. The outcome of the Iraq and Afghanistan wars contribute massively to this lack of fear. (Military planners throughout the World now understand that the US is best contained asymmetrically and that the US “usually does not get the politics behind the War”).
About the British Empire and gunboats. The British Empire was ultimately a failure because it was based on a wrong set of ideas (racial superiority, colonies serving the metropole). It collapsed like a pack of cards, exhausted after the Second World War.
Maybe the US was the only major power to realise the folly of colonial enterprise. My view is different, the US spent so much energy during the 19th Century trying to come to terms with it’s Continent-sized land mass that it barely had enough time and resources to devote to a European-style empire. There were colonial excursions (e.g. The Philippines, parts of Latin America), but unlike Britain and France the US could afford not “keep up with the neighbours” with an extensive colonial empire.
The US “feared” the USSR just as much as the USSR “feared” the US. A threat by the Soviets to intervene militarily in the war between Egypt and Israel was enough to get Kissinger on the phone with the Israelis. There are so many examples, like the trailing of the USS Enterprise by a Soviet Nuclear Sub during the India - Pakistan war or the reluctance of the US to escalate the conflict in North Vietnam for fear of drawing in the Chinese into the war. The Korean War is a classic example.