in the early 20th century? How did European colonial powers limit economic opportunities for Africans?

Because they limited economic opportunities by preventing Africans from growing crops outside of white-owned farms.

the best description of postwar writers might be progressive.

following the war, writers showed a tendency to work on artistic or social matters rather than political themes. while postwar literature may not have been the greatest period of english literature, the themes provided excellent critics a high number of novels. such examples include anthony burgess, anthony powell and frank kermode, all of which can be placed under the progressive view.