Why was the horse so significant in the development of the Plains Indian
culture?

Because people ate it.

Explanation:

They were hungry.

I was included in a lot of stories and ceremonies  and helped the Indians travel and fight easier. It was a way faster than walking

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.