Complex sentence: Thompson returned to Canada in 1958 and resumed his activities with Social Credit and soon became president of the national Social Credit Party of Canada, doing much to rebuild the party after it was shut out of Parliament in the massive Progressive Conservative landslide of 1958.
Split into simpler sentences: Thompson returned to Canada in 1958 and resumed his activities with Social Credit. He soon became president of the national Social Credit Party of Canada, doing much to rebuild the party after it was shut out of Parliament in the massive Progressive Conservative landslide of 1958.