Complex sentence: For college he went to Georgetown University's School of Foreign Service (1989), then to Harvard for a Masters degree in National Security (1992), and then to Yale for a PhD in Diplomatic and Military History (1999).
Split into simpler sentences: For college he went to Georgetown University's School of Foreign Service (1989). He then to Harvard for a Masters degree in National Security (1992), and then to Yale for a PhD in Diplomatic and Military History (1999).