This is a strong country invaded and took over another area often as a new place to live is

The right word to complete the sentence is COLONIZATION.

Colonization is to settle and take control over the autochthonous people of an area. When there is a colonization a place is appropiate for one's own use. For example the European colonization of America.

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.