In 1968, there were three television networks, ABC, CBS, and NBC (along with the precursor to PBS, NET). Television seasons started in the fall and ended as spring headed towards summer. The schedule was pretty much set in stone ... you didn't have series moving around all the time, didn't have episodes that ran 3 minutes over. Because of this, it was easy to create a schedule grid for each season, and easy for TV Guide to produce a Fall Season issue that covered pretty much everything you needed to know (not true today, when you've got the broadcast networks, the basic cable channels, the premium cable channels, the series that run 12 episodes a year, the series that always run during the summer, the series that get moved around).
As an example of how the longer seasons made a difference, consider Lancer, a Western on CBS that I can barely recall. It ran on Tuesday nights for two seasons, beginning in 1968. Like I say, we're talking a fairly obscure series. By the time Lancer finished its two-year run, there were 51 episodes. For comparison purposes, The Sopranos didn't reach Episode 51 until the next-to-last episode of Season Four.
Lancer came on at 7:30 on Tuesday nights, and was followed on CBS by The Red Skelton Hour. Skelton had been on since 1951, and had a long radio career before that. ABC countered Skelton with It Takes a Thief, which had begun as a mid-season replacement earlier in '68. NBC had a sitcom from 8:30-9:00, followed by Tuesday Night at the Movies (in those days, networks would have regularly-scheduled slots for movies ... in fact, there was a movie on one of the networks every night of the week in 1968). On September 17, 1968, the movie was the three-year-old I'll Take Sweden with Bob Hope.
The NBC sitcom on Tuesday nights that year had its premiere on September 17. Julia starred Diahann Carroll as a nurse and single mom (her husband had died in Vietnam). By 1968, Carroll, in her early 30s, had won a Tony, been nominated for an Emmy, had recorded seven albums, and made half-a-dozen movies, including Carmen Jones and Porgy and Bess. She even went to high school with Billy Dee Williams (it was the "Fame" high school). She was, in short, a star, not top-level but certainly well-known and highly-regarded. But history will likely always think of her first as the lead in Julia. Why? Because Julia was ... well, there is some argument about the specific historic nature of the show, but Wikipedia comes close enough when it calls the show "one of the first weekly series to depict an African American woman in a non-stereotypical role." Julia wasn't the first sitcom to star an African American actress ... in the early 50s, Ethel Waters had starred as a maid in Beulah, which was criticized for its "Mammy" stereotype. (Beulah, as a character and later as a series, began on radio, with Beulah played by a white male.) It took fifteen years after Beulah for another series starring a black woman: Julia.
Julia lasted three seasons and 86 episodes. Diahann Carroll won a Golden Globe award for her performance. But Carroll is said to be the reason the series was canceled ... she said she was tired of the controversy surrounding the show, which was criticized for its supposed lack of political content. Time Magazine, of all places, suggests the context under which the series operated:
Diahann Carroll, in her own series, is a black registered nurse who is trying to make it in whitey's world. Widowed Julia has a five-year-old son Cory, played by a winning little fellow named Marc Copage. They are pretty well off, judging from the nifty apartment they occupy. Still, Julia needs a job. She is turned away by America's only personnel director who is not desperate to hire Negroes. Fortunately, she finds a protector in cantankerous Dr. Chegley (Lloyd Nolan), who doesn't care what color she is as long as she knows her business. Some of Julia's problems are black, but her aspirations and life-style are white. That factor, despite NBC's laudable decision to bring Negroes more prominently into television, makes Julia hardly more than a small-screen Guess Who's Coming to TV?