Complex sentence: Born in Warsaw, his earlier poems portrayed the instability that existed in Poland after World War I. Before World War II, he was a supporter of Stalinism and joined the Communist party; he served with Soviet forces on the Eastern Front during the war.
Split into simpler sentences: Born in Warsaw, his earlier poems portrayed the instability that existed in Poland after World War I. Before World War II, he was a supporter of Stalinism and joined the Communist party. He served with Soviet forces on the Eastern Front during the war.