Complex sentence: Pursuing traditions of his family, as a youth he joined foreign military and in the years 1628-1632 he fought in the Thirty Years' War in the Holy Roman Empire in the armies of the Catholic League, commanding a cavalry unit under Albrecht von Wallenstein.
Split into simpler sentences: Pursuing traditions of his family, as a youth he joined foreign military. In the years 1628-1632 he fought in the Thirty Years' War in the Holy Roman Empire in the armies of the Catholic League, commanding a cavalry unit under Albrecht von Wallenstein.