Look at the cover and the blurb. History books usually have a more serious, academic - looking cover and the blurb will mention historical events, periods, or figures. Fiction might have a more creative or eye - catching cover and the blurb will introduce fictional characters or a fictional plot. For example, a book with a picture of an old map and a title like 'The History of the Roman Empire' is likely a history book. A book with a picture of a mysterious - looking character and a title like 'The Secret of the Lost City' is probably fiction.
Check the publisher's description and the categorization. In a bookstore, books are usually grouped in sections. If it's in the history section, it's likely a history book. But also read the publisher's short description. A history book will often state that it's based on research, real events, etc. Fiction will be described as a story created by the author. For instance, if the description says 'This book explores the real - life events of the American Civil War' it's a history book. If it says 'A thrilling adventure of a fictional hero in a made - up world' it's fiction.