OK, after thinking it over and looking up some titles to jog my memory, I've come up with a list of films that I think says something about the nature and development of the USA, that provides at least some historic insight into what made us what we are. These films are not 100% historically accurate; some I suspect are not even 10% accurate, but they do at least capture the spirit or mood of the country at a particular point. The titles in boldface are the ones I think tell our story best:
Exploration and settlement: Seven Cities of Gold (1955), The Plymouth Adventure (1952), The Black Robe (1991) (Yes, I know--French Canadian, but those priests also worked among Indians on the US side of the border).
French and Indian Wars: Allegheny Uprising (1939), Northwest Passage (1940), The Last of Mohicans (1992).
The American Revolution: The Crossing (2000)
War of 1812: The Buccaneer (1958), The President's Lady (1953)
Westward Expansion: Man in the Wilderness (1971), Rachel and the Stranger, Westward the Women
Civil War: Abe Lincoln in Illinois (1940), Glory (1989), Gone With the Wind (1939), Horse Soldiers (1959), Gettysburg (1993), Seven Angry Men (1955), The Raid (1954), The Red Badge of Courage
The Indian Wars: Little Big Man (1970), The Searchers (1956), The Unforgiven
Immigrants and Labor: The Molly Maguires (1970), Ballad of Gregorio Cortes (1982)
Wild West: The Long Riders (1980), The Westerner (1940), Along Came Jones, Monte Walsh, Shane
World War I: The Big Parade (1925), Lafayette Escadrille (1958), Sergeant York (1941), Wings (1927); All Quite on the Western Front (yeah, it’s told from the German side, but the original film version is the best WWI film there is), Paths of Glory (and this is set in the French Army, but some American GIs fought in French units, and it’s the second best WWI film).
The Great Depression: Our Daily Bread (1934), Pretty Boy Floyd (1960), Dillinger (1945) (1973), Cinderella Man (2005), Seabiscuit (2003), Wild River (1960), Grapes of Wraith,
World War II: For Whom the Bell Tolls (the Spanish civil war leading up to WWII), Above and Beyond (1952), Battleground (1949), Battle Cry, The Glenn Miller Story (1953), Guadalcanal Diary (1943), The Halls of Montezuma (1950), Judgment at Nuremberg (1961), A League of Their Own (1992), The Longest Day (1962), A Walk in the Sun, Oppenheimer (1982), Pride of the Marines (1945), The Story of G.I. Joe (1945), The Sullivans [Fighting Sullivans] (1944), Thirty Seconds Over Tokyo (1944), Tora, Tora, Tora (1970), Zoot Suit (1981), A Soldier’s Story
Korea: The Bridges of Toko-Ri (1954), Manchurian Candidate (1962), Pork Chop Hill (1959), Retreat, Hell! (1952), The Steel Helmet
20th Century politics and such: All the King's Men (1949), All the President's Men (1976), Citizen Kane (1941), Give 'Em Hell, Harry! (1975); The Great White Hope (1970), Hoffa (1992), Inherit the Wind (1960), Malcolm X (1992), Murder, Inc. (1960), Raging Bull (1980), The Right Stuff (1983), Sacco and Venzetti (1970), Salt of the Earth (1954), Spirit of St. Louis (1957), Sunrise at Campobello (1960), Tail Gunner Joe (1977), The Front (1976), Wind and the Lion (1975),
Vietnam: Full Metal Jacket (1987)