He takes a broad-brush approach to the study of history.
A broad-brush approach, strategy, or solution deals with a problem in a general way rather than concentrating on details. He's giving a broad brush approach to the subject
To describe a class of objects or a kind of phenomenon in general terms, without specific details and without attention to individual variations
Painting slavery with a broad brush in literature, film and even political debate has kept us from knowing the real horror and heroism of the institution.