Historically-Minded; Journalistic
One of the primary purposes of Roots is to connect people with the mind-explodingly awful historical reality of slavery in America, especially as it relates to the cultural traditions of those who were imprisoned by the institution. As a result, many of the novel's events and characters reflect this historical context and are used to reveal broader societal truths. This relation between the personal experiences of individuals and wider historical forces is a huge aspect of Alex Haley's writing style.
We also see a lot of influence of Haley's career as a journalist in Roots. Haley isn't really interested in crafting hyper-dense metaphors or dropping mind-bending meta-fictional techniques. Instead, his strength lies in his ability to depict cultures and relate them to historical events, as well as his ability to probe the psychology of individual characters. This style places the focus on content rather than form, and it's the perfect choice for a piece of historical fiction like Roots.