Like if you are from a not very represented country makes you more likely to be accepted than someone from represented countries ( like China or India)
If you are very qualified and the decision is between underrepresented applicant and a person from overrepresented country( they can admit both of them based on their achievements and personality) they would go with the first one to add diversity.
But you still need to be top student in all terms. If you are not qualified for insert the name college, your country will not help you.
The absence of a negative is not necessarily a positive. A student applying to the name-brand universities from China and India has more competition, simply b/c there are so many super-qualified candidates. A student applying from (say) Myanmar or Paraquay, will be competing with only a tiny number of local applicants- but you still have to be as good as the best from China, India or anywhere else.
This applies very much to the most famous names. Once you get to less well-known names there is more room to stand out.