Complex sentence: With Venizelos' arrival, the League was sidelined, and the energetic and relatively young politician soon dominated Greek political life, carrying out a large number of overdue reforms, including the creation of a revised constitution.
Split into simpler sentences: With Venizelos' arrival, the League was sidelined, and the energetic and relatively young politician soon dominated Greek political life. His government carried out a large number of overdue reforms, including the creation of a revised constitution.