Here the metonym "nation" refers to the people of the nation. Alternate translation: "afflict the people of the nation" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The psalmist speaks of powerful people treating powerless people badly as if it were crushing them or breaking them in pieces. See how "break in pieces" is translated in [Psalms 72:4](../072/004.md). Alternate translation: "They completely destroy" or "They greatly harm" (See: [[rc://en/ta/man/translate/figs-metaphor]])