Oppressive governments frequently imprison political opponents.
Literal
Oppressive government [topic-は] frequently political-enemies [object-を] imprison.
圧政的 'oppressive' uses the suffix ~的 to make an adjective from the noun 圧政 'tyranny.' 政敵 'political enemy/opponent' — 政 'politics' + 敵 'enemy.' 投獄する 'to imprison' — 投 'throw' + 獄 'prison.' All Sino-Japanese compounds, giving the sentence a formal, news-report quality.