1 (a) People in Taiwan are nice and friendly. (b) Students in the U.S.A. have to go to school 195 days a year. These are very general statements.
2 (a) The people in Taiwan are nice and friendly. (b) The students in the U.S.A. have to go to school 195 days a year. These are more specific. eg They suggest a context like: The people in Taiwan are
There is no difference in meaning. Since there are so many people in Taiwan - millions of them - the article can be omitted. You wouldn't omit it in the following structurally similar sentences in which the reference is to a small number of people or a small amount of something:
The people in this room are nice. The boys in the courtyard are playing football. The water in