Why would your history textbook include a chapter about geography economics and civics?

Think of history as an umbrella, and geography as the rainy weather. Everything that happens, happens within the context of history: economics, civics, politics, etc. They are all affected by the place and time within history.

Geography then plays a role in how history develops. Without certain geographical situations and circumstances, moments in history may not have been possible. For example, the beginning of historical civilization has its roots in five specific geographical locations in the world (Mesopotamia, Egypt, the Indus River Valley, China, and the Americas). Without such geography that enabled the development of these civilizations (rivers being the most important geographical feature, as the water sustained life and allowed for irrigation to water crops), life as we know it would be radically different today.

Such a textbook takes an interdisciplinary approach to studying history; that is, it looks at the historical impact of these three disciplines within the broader scope of history. It allows for a more complete and complex view. Changes do not happen independent of one another. Each plays a role and every change in one area, affects the other.