About film and history
Many people get their ideas about history from film (and TV). How history is represented in films is therefore of great importance.
For most people watching films, including even film critics, the historical accuracy is not the main question in deciding whether a film is a good one. Here we are thinking about the concerns of historians, however.
Fiction and non-fiction
"Fiction" means made-up stories. "Non-fiction" means accounts that claim to be literally true descriptions of the world. For example, the Harry Potter stories are fiction: the events are completely imaginary. But the biography Seretse Khama is non-fiction: the authors are claiming that the events are all real. Of course, a work of "non-fiction" might contain mistakes or untrue material, but it is supposed to be true.
Fiction is different from life. Stories are supposed to make sense; we expect them to have some sort of ending even if it is an unclear one. People's actions are supposed to be connected to their character. But life does not have to make sense. Events might go nowhere; a person might do something out-of-character for no reason we can understand. In this way fiction is actually more limited than real life (even though although fiction can include impossible events).
Film includes both categories, but also sometimes mixes them. (Most fiction is of course not connected to history but is about the present.)
We might classify the basic categories of film in terms of their relationship to history like this. (Note however that in practice films may not quite fit neatly into one category.)
A documentary presents a factual account. Documentaries are often narrated, and typically prefer to use original films or photographs. Documentaries are more common on TV than cinema film. A documentary is a bit like a non-fiction book. Examples: The Africans (1980s, Ali Mazrui), They Shall Not Grow Old (2014, about the First World War). Documentary tries to present accurate history.
Also called dramatized documentary. A docudrama presents real events, but portrays them with actors as with an ordinary film. As far as possible it keeps to the known facts. It may make some changes to make the film easier to follow—for example, it might combine two or more people into one person—but these should be limited and the main events should keep to the facts. Examples: Stalin (1992), Apollo 13 (1995). Docudrama tries to present generally accurate history, in an accessible form.
Historical fiction is fiction, but set in some real historical environment. Most often the major events are used as background, with a story about fictional characters who are often not important people. A story about ordinary people in some situation (a war, etc.) can convey knowledge and ideas about the real events, though this is not always the intention. Historical fiction is perhaps more common in books (e.g. Lauri Kubuitsile, The Scattering, about the Namibian genocide) than in film. Although it may be about some event, as with The Scattering, sometimes the focus is what was life in a particular time and place. Example of historical fiction in film: Master and Commander (2003), which portrays the life of naval warfare at the beginning of the 19th century. Historical fiction typically uses accurate history, but does not focus on the main historical events.
"Based on real events", or fictionalized history:
There is no fully established term for this. I will call it fictionalized history. Fictionalized history is the most problematic type, though not all such films are bad.
These films present real events, or things claimed to be real events, but significantly alter the facts. This is done for several reasons. The most obvious is to create a good story. The film Enigma (2001, screenplay by Tom Stoppard from a novel by Robert Harris) depicts the (real) Bletchley code-breakers in the Second World War quite well, but introduces a fictional spy story. (Enigma might alternatively be considered historical fiction: the line is not always clear.) However the changes can also have implications. Enigma doesn't alter the significance of Bletchley, but the genius Alan Turing, who was gay, was replaced by a heterosexual character. My guess is that the change reflected the needs of the plot rather than any bias on the part of the author, but not long after this film, Turing's later prosecution for homosexuality became a symbol of the persecution of gay men, and he was given a posthumous pardon and apology. Hence, the substitution now prompts questions. The spy being Polish also seems rather unfair given the actual role of the Poles.
As I noted under dramatized documentary, films may change peripheral things for the sake of the main story. But what is peripheral? The film A United Kingdom, about the marriage of Seretse Khama and Ruth Williams, was I think intended to be reasonably accurate about the marriage. The marriage was regarded as the point of the story. But the film altered facts about Tshekedi Khama, the Bangwato regent who opposed the marriage, and about some other issues, in ways which people in Botswana found unsatisfactory. Who is to say what are the important and unimportant details? Inevitably, the film-makers.
American films sometimes show the United States as having a more important or more positive role than was really the case. In the film U-571, a film depicted American military forces doing something which was actually the achievement of British forces, which led to public outrage in the UK. American attitudes to Britain are complicated, uneasily mixing a positive relationship with traditional suspicion, often involving mythologized versions of the American Revolution. (An amusing instance occurs in Star Wars, where the Imperial officers sound British and the rebels sound American, though the roles of the great actors Alec Guinness and James Earl Jones go against this.) This is not universal, though: an interesting case is the Shirley Temple film The Little Princess (1939) which has an emotional British-patriotic ending, probably related to the date.
Sometimes fictional events are portrayed that cause offence with no discernible artistic or even propagandistic purpose, which may reflect sheer carelessness as much as indifference to truth. Makers of film and TV sometimes indulge in a sort of convenient ambiguity whereby they will claim that their work is "researched", or "true in spirit", but when challenged but will change to the line that "everyone knows" it is fiction. Sometimes the changes are so great that the story becomes quite different from real history, as with Elizabeth (1998), which was described by a critic as taking names and facts about Elizabeth I and arranging them at random.
The concept of a film "based on real events" is also used in non-historical films. Audiences often think that when the film claims to be "based on real events" it means that something more or less like the film happened, but in fact this may not be the case at all. The "real events" gave the film-makers an idea, but the story in the film may be different.