A notable movement in US television around the turn of UsefulNotes/TheSeventies--"one of the earliest efforts at [[NetworkDecay channel drift]]", [[https://en.wikipedia.org/wiki/Rural_purge according to]] [[Wiki/{{Wikipedia}} That Other Wiki]]--when the AC Nielsen company made changes to give networks and advertisers a clearer picture of just who (as well as how many people) watched which shows. At the time, many popular programs (such as ''Series/GreenAcres'' and ''Series/HeeHaw'') were rural-themed and were skewing more towards viewers from rural areas or just an older demographic in general (as opposed to younger "urban" viewers, who wanted more contemporary and innovative programs). That, along with the implementation of the Prime Time Access Rule in 1971 (which made the 7:00 PM ET hour off-limits to network programming, forcing the traditional start of primetime to move from 7:30 PM to 8:00 PM, and making the 7:00 PM hour a lot more lucrative for syndicated shows), led the networks to perform some spring cleaning to make room for more modern fare.

The purge began in 1970 with the cancellation of ''Series/PetticoatJunction'' by Creator/{{CBS}}; to be fair, the series' viewership had been declining since the death of its star Bea Benaderet. CBS was by far the biggest offender in the purge, cancelling a large array of {{Long Runner}}s just because they skewed too old. Actor Pat Buttram of ''Green Acres'' (which, unsurprisingly, got canned) famously commented that CBS "canceled every show that had a tree in it-- including ''Series/{{Lassie}}''."

Despite its name, the resulting carnage was not exclusively aimed towards rural shows; the casualties of the purge included several long-running [[TheWestern westerns]] (including ''Series/{{Bonanza}}'', though the genre had been in a decline due to MoralGuardians complaining about their violence, and ''Bonanza'' itself was facing declining ratings due to the death of co-star Dan Blocker) and variety shows (such as ''The Jackie Gleason Show'', ''The Lawrence Welk Show'', and ''The Red Skelton Show''; the latter got SavedByTheNetwork for one more season on Creator/{{NBC}}), while CBS and Creator/{{ABC}} each killed two birds with one stone by cancelling the rural variety shows ''Hee Haw'' and ''The Music/JohnnyCash Show''. Both ''Hee Haw'' and ''The Lawrence Welk Show'', however, got UnCancelled and proved to be popular in syndication, with ''Hee Haw'' lasting all the way through 1992.

Ironically, the biggest subversion of the purge was the 1972 CBS rural drama ''Series/TheWaltons''; produced in response to Congressional hearings on the quality of TV programming following the purge, it was slotted in a [[FridayNightDeathSlot death slot]] against popular Thursday-night programs ''Series/TheModSquad'' on ABC and ''The Flip Wilson Show'' on NBC under the presumption that it would probably be cancelled quickly. Instead, it lasted ''nine'' seasons, peaked as the second-highest rated program on television in its 2nd season, and launched the successful Creator/{{Lorimar}} studio.

It should be noted that had Nielsen's finer-grained information become available a few years earlier, ''Series/StarTrekTheOriginalSeries'' and ''Series/TheSmothersBrothersComedyHour'' would no doubt have run longer; they attracted the well-educated younger viewers advertisers crave, but nobody knew it at the time and saw only mediocre total-viewership numbers for the former and the latter's battles with ExecutiveMeddling would have been easier to endure if the network had the later audience priorities.

!!Some of the shows cancelled in the purge included:
* ''Series/MayberryRFD'' (CBS, 196871)
* ''Series/TheBeverlyHillbillies'' (CBS, 196271)
* ''Series/TheEdSullivanShow'' (CBS, 194871)
* ''Series/GreenAcres'' (CBS, 196571)
* ''Series/HeeHaw'' (CBS, 196971; revived in syndication, where it ran until 1992)
* ''Series/TheVirginian'' (NBC, 1962-1971)
* ''Series/HogansHeroes'' (CBS, 196571)
* ''Series/MyThreeSons'' (ABC, 1960-1965; CBS 1965-1972)
* ''American Scene Magazine'' / ''The Jackie Gleason Show'' (CBS, 196270)
* ''The Music/JohnnyCash Show'' (ABC, 196971)
* ''Series/{{Lassie}}'' (CBS, 195471; moved to syndication, where it ran until 1973)
* ''The Lawrence Welk Show'' (ABC, 195571; moved to syndication, where it ran until 1982)
* ''Series/PetticoatJunction'' (CBS, 196370)
* ''Series/MutualOfOmahasWildKingdom'' (NBC, 1963-1971, moved to syndication with new episodes produced until 1987)
* ''The Andy Williams Show'' (NBC, 1962-1971 followed by a brief run in syndication)
* ''The Red Skelton Show'' (CBS, 195370; moved to NBC, ending in 1971); it ranked #7 for the 1969-70 season, making it the highest-rated show ''ever'' to be cancelled in television history up to that point

Nonetheless, the purge set the stage for a number of new shows to be introduced to the network lineups, some of which became legendary on their own.

!!Some of the shows which the purge made room for included:
* ''Series/AllInTheFamily'' (CBS, 197179)
* ''Series/TheBobNewhartShow'' (CBS, 197278)
* ''Series/{{MASH}}'' (CBS, 197283)
* ''Series/TheMaryTylerMooreShow'' (CBS, 197077)
* ''{{Series/Maude}}'' (CBS, 197278)