Complex sentence: Shortly thereafter, he was replaced as party leader by Stanisław Kania and jailed for a year in December 1981 by the next ruler of Poland was General Wojciech Jaruzelski, who introduced martial law on December 13,1981.
Split into simpler sentences: Shortly thereafter, he was replaced as party leader by Stanisław Kania and jailed for a year in December 1981. The next ruler of Poland was General Wojciech Jaruzelski, who introduced martial law on December 13,1981.