Chapters in history can be divided into ERAS, which are periods of time that are characterized by certain events or developments. ERAS can range from the prehistoric era to the modern era, and each era is further divided into smaller units of time. For example, the Middle Ages is an era that is divided into the Early Middle Ages, High Middle Ages, and Late Middle Ages. Each of these ERAS has its own unique set of events and developments that shaped the course of history.