Composers often used what to add national elements to their music

Different instruments native to that country or region

They use musical ideas and motifs that are inspired by the nation which they are composing for. This usually comes from the folklore tradition and incorporates not only various themes, but also various instruments. For example, a Scottish national composition would surely include bagpipes as an instrument since it's traditionally associated with the area.

The artist above used rapid brushstrokes 

The trumpet isn't part of the folk rock instrument groups!