Complex sentence: In 1981 he played a key role in imposing martial law and crushing the "Solidarity" movement in Poland, but eight years later he presided over the country's transition to democracy as its last Communist prime minister.
Split into simpler sentences: In 1981 he played a key role in imposing martial law and suppression the "Solidarity" movement in Poland. But eight years later he presided over the country's transition to democracy as its last Communist prime minister.