QED is an example of a quantum field theory. It's a theory of fields spread out over all of space and time. Particles are derived concepts... They're excitations of the underlying field.

I know. When I wrote that there's no continent called America, I was including that with "in most standard forms of English..." (even though it's arguably not about language). The naming of continents is done differently in different places and has also changed over time. But most English-speaking countries currently don't count America as one continent. It's arbitrary but it is a convention, and that strongly influences how the language is used.

In most standard forms of English, "America" refers unambiguously to the USA. There is no continent called America. Instead, there are the continents of North America and South America. You can refer to both of these continents together as "the Americas," but there is no standard adjective for people from there. The best that you can do is to refer to "North Americans" or "South Americans." This is different in (at least some forms of) Spanish and German, but kindly note that although some words in your language and in English might be very similar, their meanings are not identical.