Scholars did not employ the term "nonprofit sector" as a category until the 1970s. "Although there was a vast literature on particular kinds of nonprofits—charities, education, hospitals, museums, social welfare, and so on," historian Peter Hall has written, "no effort was made before the 1970s to treat these as part of a unified sector of activity." 1 When they did so, they grouped many different sorts of nonprofit activities together based on one benefit that most of them had in common—tax exemption.