Complex sentence: After leaving the Liberal Party, he founded the Mouvement Souveraineté-Association, which later merged with another sovereigntist party, the Ralliement National of Gilles Grégoire, to create the Parti Québécois in 1968.
Split into simpler sentences: After leaving the Liberal Party, he founded the Mouvement Souveraineté-Association. The MSA would merge with another sovereigntist party, the Ralliement National of Gilles Grégoire, to create the Parti Québécois in 1968.