Complex sentence: Nikephoros Botaneiates had served as general under Constantine IX and Romanos IV Diogenes, and under Michael VII Doukas he became governor of the Anatolic theme and commander of the troops in Asia.
Split into simpler sentences: Nikephoros Botaneiates had served as general under Constantine IX and Romanos IV Diogenes. Under Michael VII Doukas he became governor of the Anatolic theme and commander of the troops in Asia.