During world war i, was the term widely used to describe a state of war in which neither side was winning or gaining an advantage.

The answer is stalemate.  Neither side had the advantage as both armies remained in the trenches and were unable to advance. It was only during  the entry of the United States that the tide of the war  began to turn.

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.