Alternative history, sometimes known as counterfactual history, is a literary genre that explores alternate versions of historical events that did not happen in reality. Other synonyms for alternative history include speculative fiction, historical fantasy, and what-if history. While many alternative history stories incorporate real historical figures and events, they often take liberties with the actual facts to create a new narrative. Many alternative history stories explore questions such as "what if Germany won World War II?", "what if the Roman Empire never fell?", or "what if the American Revolution failed?". This genre allows readers to explore alternate worlds and outcomes, while also examining the impact of key events and decisions throughout history.