Complex sentence: He left for France, where he joined the Jesuits and became abbot of Abbey of Saint-Germain-des-Prés in Paris which resulted in the Polish-Lithuanian Commonwealth being left without a monarch, necessitating a free election.
Split into simpler sentences: He left for France, where he joined the Jesuits and became abbot of Abbey of Saint-Germain-des-Prés in Paris. As a result of his decision to abdicate, the Polish-Lithuanian Commonwealth was left without a monarch, necessitating a free election.