The modification genre that encompasses true accounts of past periods or events is typically referred to as historical nonfiction or historical narrative. This genre includes works that recount true events, people, and experiences from history with an emphasis on factual accuracy while often employing narrative techniques to engage readers. Examples include biographies, memoirs, historical essays, and accounts that provide insight into specific historical periods or events.
If you were referring to a specific literary style or format, such as memoir or documentary, those also contain true accounts but may not be exclusively tied to broader historical contexts.