Complex sentence: He immediately became the chairman of the parliamentary party, succeeding Jeltje van Nieuwenhoven, and leaving her, Klaas de Vries and Jouke de Vries behind him by a 30% margin.
Split into simpler sentences: He immediately became the chairman of the parliamentary party, succeeding Jeltje van Nieuwenhoven. Leaving Jeltje van Nieuwenhoven, Klaas de Vries and Jouke de Vries behind him by a 30% margin.