I know the question may seem too vague and weird, so let's go right to the example for more clarification:
Scholars ask the-upper-class countries to help the-lower-class in the breakout of the coronavirus.
As you see, I omitted countries after " the-lower-class" so as to be more concise. Now, did I use "the lower class", would it be wrong or it is actually more correct?
Furthermore, I'm not sure whether I can use the-lower-class or its counterparts for countries; therefore, please feel free to rectify it as well, but please don't overlook my main question, which is the first one.