War film
Genre: The war film genre is not necessarily tightly defined: the American Film Institute, for example, speaks of "films to grapple with the Great War" without attempting to classify these. However, some directors and critics have offered at least tentative definitions. The director Sam Fuller defined the genre by saying that "a war film's objective, no matter how personal or emotional, is to make a viewer feel war." John Belton identified four narrative elements of the war film within the context of Hollywood production: a) the suspension of civilian morality during times of war, b) primacy of collective goals over individual motivations, c) rivalry between men in predominantly male groups as well as marginalization and objectification of women, and d) depiction of the reintegration of veterans. The fateful nature of battle scenes means that war films often end with them.

The film critic Stephen Neale suggests that the genre is for the most part well defined and uncontentious, since war films are simply those about war being waged in the 20th century, with combat scenes central to the drama. However, Neale notes, films set in the American Civil War or the American Indian Wars of the 19th century were called war films in the time before the First World War. The critic Julian Smith argues, on the contrary, that the war film lacks the formal boundaries of a genre like the Western, but that in practice, "successful and influential" war films are about modern wars, in particular World War II, with the combination of mobile forces and mass killing. The film scholar Kathryn Kane points out some similarities between the war film genre and the Western. Both genres use opposing concepts like war and peace, civilization and savagery. War films usually frame World War II as a conflict between "good" and "evil" as represented by the Allied forces and Nazi Germany whereas the Western portrays the conflict between civilized settlers and the savage indigenous peoples. James Clarke notes the similarity between a Western like Sam Peckinpah's The Wild Bunch and "war-movie escapades" like The Dirty Dozen.
The film historian Jeanine Basinger states that she began with a preconception of what the war film genre would be, namely that:

What I knew in advance was what presumably every member of our culture would know about World War II combat films—that they contained a hero, a group of mixed types [of people], and a military objective of some sort. They take place in the actual combat zones of World War II, against the established enemies, on the ground, the sea, or in the air. They contain many repeated events, such as mail call, all presented visually with appropriate uniforms, equipment, and iconography of battle.
Further, Basinger considers Bataan to provide a definition-by-example of "the World War II combat film", in which a diverse and apparently unsuited group of "hastily assembled volunteers" hold off a much larger group of the enemy through their "bravery and tenacity". She argues that the combat film is not a subgenre but the only genuine kind of war film. Since she notes that there were in fact only five true combat films made during the Second World War, in her view these few films, central to the genre, are outweighed by the many other films that are only just war films. However, other critics such as Russell Earl Shain propose a far broader definition of war film, to include films that deal "with the roles of civilians, espionage agents, and soldiers in any of the aspects of war (i.e. preparation, cause, prevention, conduct, daily life, and consequences or aftermath.)" Neale points out that genres overlap, with combat scenes for different purposes in other types of film, and suggests that war films are characterised by combat which "determines the fate of the principal characters". This in turn pushes combat scenes to the climactic ends of war films. Not all critics agree, either, that war films must be about 20th-century wars. James Clarke includes Edward Zwick's Oscar-winning Glory (1990) among the war films he discusses in detail; it is set in the American Civil War, and he lists six other films about that war which he considers "notable". The screenwriter and scholar Eric R. Williams identifies war films as one of eleven super-genres in his screenwriters' taxonomy, claiming that all feature-length narrative films can be classified as belonging to one of them.
The British military historian Antony Beevor "despair[s]" at how film-makers from America and Britain "play fast and loose with the facts", yet imply that "their version is as good as the truth". For example, he calls the 2000 American film U-571 a "shameless deception" for pretending that a US warship had helped to win the Battle of the Atlantic—seven months before America entered the war. He is equally critical of Christopher Nolan's 2017 film Dunkirk with its unhistorically empty beaches, low-level air combat over the sea, and rescues mainly by the "little ships". Beevor feels, however, that Continental European film-makers are often "far more scrupulous"; for example, in his view the 2004 German film Downfall accurately depicted the historical events of Hitler's final days in his Berlin bunker, and he considers the 1965 French film The 317th Platoon, set in Vietnam, "the greatest war movie ever made". The 1966 film The Battle of Algiers is, he argues, a close second.

History: 

American Civil War: The costliest war in U.S. history in terms of American life, this war has been the subject of, or the backdrop to, numerous films, documentaries and mini-series. One of the earliest films using the Civil War as its subject was D.W. Griffith's 1910 silent picture, The Fugitive. Films that have the war as its main subject, or about a certain aspect of the war, include the 1989 film Glory, about the first formal unit of the Union Army during the American Civil War to be made up entirely of Black volunteers. Some films such as Gettysburg focused on a single battle during the war, or even on a single incident, like the French short film La Rivière du Hibou (An Occurrence at Owl Creek Bridge) and Disney's The Great Locomotive Chase (1956).  Others like the 1993 miniseries North and South spanned the entire breadth of the war. Some films deal with the human aspects of the war, such as The Red Badge of Courage (1951), or Shenandoah (1965), on the tragedy that the war inflicted on the civilian population. Ken Burns's The Civil War is the most-watched documentary in the history of PBS.

The Spanish–American War: The first war films come from the Spanish–American War of 1898. Short "actualities"—documentary film-clips—included Burial of the Maine Victims, Blanket-Tossing of a New Recruit, and Soldiers Washing Dishes. These non-combat films were accompanied by "reenactments" of fighting, such as of Theodore Roosevelt's "Rough Riders" in action against the Spanish, staged in the United States.

First World War: During the First World War, many films were made about life in the war. Topics included prisoners of war, covert operations, and military training. Both the Central Powers and the Allies produced war documentaries. The films were also used as propaganda in neutral countries like the United States. Among these was a film shot on the Eastern Front by official war photographer to the Central Powers, Albert K. Dawson: The Battle and Fall of Przemysl (1915), depicting the Siege of Przemyśl, disastrous for the Austrians, with incidents reenacted using soldiers as extras.
The 1915 Australian film Within Our Gates (also known as Deeds that Won Gallipoli) by Frank Harvey was described by the Motion Picture News as "a really good war story, which is exceptional".

The 1916 British film The Battle of the Somme, by two official cinematographers, Geoffrey Malins and John McDowell, combined documentary and propaganda, seeking to give the public an impression of what trench warfare was like. Much of the film was shot on location at the Western Front in France; it had a powerful emotional impact. It was watched by some 20 million people in Britain in its six weeks of exhibition, making it what the critic Francine Stock called "one of the most successful films of all time".
The 1925 American film The Big Parade depicted unglamorous elements of war: the protagonist loses his leg, and his friends are killed. William A. Wellman's Wings (1927) showed aerial combat during the war and was made in cooperation with the Army Air Corps. It proved a powerful recruiting tool. It became the first film (in any genre) to be awarded an Oscar for best picture. Later films of varied genres that deal with the First World War include David Lean's "colossal epic", both war film and biopic Lawrence of Arabia (1962), shot in the then unfamiliar and exciting 70mm Technicolor, and described by Steven Spielberg as "maybe the greatest screenplay ever written for the motion-picture medium"; Richard Attenborough's satirical anti-war musical comedy based on Joan Littlewood's play of the same name, Oh! What a Lovely War (1969); Spielberg's 2011 war drama War Horse was based on Michael Morpurgo's children's novel of the same name.