Complex sentence: In the 1960s, the Québécois wing of the party split off to form the "Ralliement créditiste", and although the two wings reunited in 1971, the party was ultimately left without any parliamentary seats following the 1980 federal election, and thereafter declined into irrelevance.
Split into simpler sentences: In the 1960s, the Québécois wing of the party split off to form the "Ralliement créditiste". Te party was left without any parliamentary seats following the 1980 federal election, and thereafter declined into irrelevance.