My teacher says there's more than one kind of history. How can that be?

History texts and many articles deal with a few areas of historical study: political, economic, social, and intellectual history. Today, many new fields have become objects of study by historians.  These include ethnic history, women's history, environmental history, and psychohistory (which seeks to explain the past by examining the motives of individuals).
History as an academic discipline in the United States is just over a century old. While most historians teach, others make their livelihood outside of the college or university community. Public, or applied history is a comparatively new field. Public historians are not based in a university but work for government agencies, private corporations, historical societies and museums, and as independent consultants. They may develop corporate archives, write a company or agency history, provide expert testimony in a lawsuit, or tackle numerous other assignments that involve the application of the historian's research and analytical skills to real-world issues.