They're not. There are however two factors greatly biasing your perception of UFOs. First, it takes a fair amount of effort to track down information in foreign language sources, so in general there's going to be a lot less English-language information on Chinese, Russian, or Japanese reports of UFOs. Second, militaries are going to both generate more UFO reports (thanks to military research programs that go awry, e.g., the circumstances behind the Roswell incident) and be a lot more open to collecting and investigating them (because of their ability to indicate the previous point). The US military being the largest and most well-funded in the world is thus going to generate the largest UFO report halo around it.
The "alien mummies" and "Buga sphere" came from South America, for instance. You can find UFO and alien contact reports from all over. Brazil has the Varginha incident, the Ariel School incident in Zimbabwe, the Voronezh UFO incident in Russia, Japan Airlines Flight 1628, to name a few examples. The UFO phenomenon isn't at all limited to the US.
Although to be fair, all of that's probably the result of American pop cultural influence.
It plain isn't and to claim that it is shows that you have done EXACTLY 0 research into the topic. This kind of bad faith engagement shows an utter lack of curiosity.
UFOs are huge in South America within just seconds you can find hundreds of sightings and discussions about them:
https://en.wikipedia.org/wiki/Varginha_UFO_incident
https://en.wikipedia.org/wiki/UFO_sightings_in_Brazil
https://www.vice.com/en/article/i-went-alien-hunting-on-chil...
Ufos are also a thing above Europe with the Belgian Ufo wave and the Rendlesham Forest incident being well known and seminal cases in UFO Lore
https://en.wikipedia.org/wiki/Rendlesham_Forest_incident
https://en.wikipedia.org/wiki/Belgian_UFO_wave
Africa also had for example the ariel school incident in Zimbabwe, one of the most well known UFO cases ever
https://en.wikipedia.org/wiki/Ariel_School_UFO_incident
https://en.wikipedia.org/wiki/UFO_sightings_in_Africa
Same goes for russia where after the cold war ufo sightings were discussed in offically declassified documents:
https://www.cia.gov/readingroom/docs/DOC_0005517761.pdf
Must I go on or is that enough to accept that "UNKNOWN THING IN SKY DOES WEIRD THING I DON'T UNDERSTAND" is pretty much a global phenomenon that can and should be scientifically investigated just the same as we would investigate everything else we find anomalous?
What are your thoughts about multiple pilots in formation seeing things that are corroborated by optical, laser, and radar sensors used by the local aircraft and remote radar platforms?
Because that's where things get fun! :)
You don't notice it do you? Re-read again what I wrote. At no point did I argue that it's aliens. Intentionally.
You first point was proven wrong instantly "it's only an USA Phenomenon". You don't bother to research anything but stick with your hypothesis. You don't even go look for evidence yet are utterly convinced of the result of your complete lack of research.
Here's an example of metal alloy that's supposed to come from an UFO and shows an interesting composition we cannot replicate. It's a well known artefact:
https://tothestars.media/de-de/blogs/press-and-news/tts-anal...
It had some analysis done by different researchers https://www.researchgate.net/publication/237233241_Compositi...
Your lack of curiosity is still very obvious.
Everything is aliens and a government cover up to those folks....even when you prove it's a floating trash bag they think you're a fool. There are a few rational commenters, but a lot of people that want to believe so bad they fall for all these grifters selling pseudoscience books and seminars.
That's a pretty annoying sampling bias and doesn't reflect the community as a whole. There's plenty of rational voices that think most things are just balloons and drones, but they don't comment when it's boring and mundane. In those cases, only schizo voices remain.