Here the metonym "a nation" means the people from a nation. Alternate translation: "people from a nation" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The words "oppressed" and "crushed" mean basically the same thing. This can be stated in active form. Alternate translation: "they will always oppress and crush you" or "they will oppress you continually" (See: [[rc://en/ta/man/translate/figs-doublet]] and [[rc://en/ta/man/translate/figs-activepassive]])