Nostalgia is not the same as history. The folks at the History Channel should know that. If you’re looking for a pleasant and diverting glance back at the Western movie genre, then the two-hour documentary “When Cowboys Were King” (7 p.m., History) is for you. But let’s not call it history.

“Cowboys” presents a rich collection of film clips, beginning with Thomas Edison’s very first feature film, “The Great Train Robbery,” shot in New Jersey in 1903. The documentary dutifully trots out brief biographies of Western movie stars, including Tom Mix, William Boyd, Buck Jones, and, of course, the singing cowboys Tex Ritter, Gene Autry and Roy Rogers. The late John Ritter (son of Tex) is among those interviewed here. Roy Rogers’ son Dusty discusses his father’s virtual servitude to the old Republic Pictures studio.

“Cowboys” concentrates on the B Westerns: the thousands of thrilling, if forgettable, films that filled the seats of America’s movie houses back when they showed double bills and changed their offerings twice a week. But it often fails to discuss the films in any larger context. Sure, the singing Westerns of the late 1930s seem odd, but no more so than the many operetta-influenced films of the period, when Jeanette McDonald and Nelson Eddy ruled the box office.

“Cowboys” is particularly shallow when discussing the decline of the Western. Did young viewers in the 1960s reject the “traditional values” of men in white hats? Or recoil from the genre’s rather glib racism and antiseptic screen violence? Have gangster movies of the post-“Godfather” era replaced the Western as the modern shoot-’em-up? (“Sopranos” viewers would think so, based on the number of times Tony Soprano invokes the memory of Gary Cooper or falls to sleep watching “Rio Bravo.”) The Western movie and cowboy image continue to evoke powerful and contradictory responses. Just don’t go looking for a thoughtful discussion of them in this History Channel offering.

Tonight’s other highlights

• Members of Drake and Morgan seethe as two of the Outcasts become part of the in-crowd on “Survivor: Pearl Islands” (7 p.m., CBS).
• A firefighter dies during a heroic rescue on “Tru Calling” (7 p.m., Fox). Or does he?
• A small-town dog digs up a human skull on “CSI” (8 p.m., CBS).
• A seemingly well-adjusted teen vanishes on “Without a Trace” (9 p.m., CBS).
• Pratt and Kovac debate the ethics of trying to save a premature infant on “ER” (9 p.m., NBC).
• Scheduled on “PrimeTime” (9 p.m., ABC): an interview with Pink; nightclub safety; a kidnapping “victim” whose friends claim was a willing participant and part of a scripted movie.

Late night

Iggy Pop and Sum 41 appear on “Late Show with David Letterman” (10:35 p.m., CBS) … Jay Leno welcomes Russell Crowe, Steve Irwin and ZZ Top on “The Tonight Show” (10:35 p.m., NBC).