According to Wikipedia, the discipline of 'Social Studies' is intended to endow the student with 'civic competence'. The key is in the broad term 'Social', meaning society, a collection of more than one human being. Human interactions require mutually agreed upon rules of behavior and, in large numbers. these mutually agreed upon rules of behavior ensured by a form of government. There can be no civilization without government (this by no means indicates that all forms of government are just or desirable).
In order to understand the nature of the society one lives in and the government by whose rules one lives, an individual needs to understand the history of that society and that government. In turn, one cannot understand history without understanding geography by which the events history are shaped. Thus the central place occupied by the subjects of history and geography within the discipline of Social Studies.