A notable movement in US television around the turn of TheSeventies 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 ''GreenAcres'' and ''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}} (although in fairness, the show had been faced with declining viewership since the death of star Bea Benederet). 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, [[CaptainObvious unsurprisingly]], got canned) even once commented that CBS "canceled every show that had a tree."

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'' 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 JohnnyCash Show''. ''Hee Haw'' however, got UnCancelled and proved to be popular in syndication, lasting all the way through 1992.

It should be noted that had Nielsen's finer-grained information become available a few years earlier, ''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/TheAndyGriffithShow'' / ''MayberryRFD'' (CBS, 1960-68/1968-71)
* ''Series/TheBeverlyHillbillies'' (CBS, 1962-71)
* ''Series/{{Bewitched}}'' (ABC, 1964-72)
* ''{{Series/Bonanza}}'' (NBC, 1959-73)
* ''Series/TheBradyBunch'' (ABC, 1969-74)
* ''The Ed Sullivan Show'' (CBS, 1948-71)
* ''Series/GreenAcres'' (CBS, 1965-71)
* ''Series/{{Gunsmoke}}'' (CBS, 1955-75)
* ''HeeHaw'' (CBS, 1969-71; revived in syndication, where it ran until 1992)
* ''Series/HogansHeroes'' (CBS, 1965-71)
* ''American Scene Magazine'' / ''The Jackie Gleason Show'' (CBS, 1962-70)
* ''The JohnnyCash Show'' (ABC, 1969-71)
* ''Series/{{Lassie}}'' (CBS, 1954-71)
* ''The Lawrence Welk Show'' (ABC, 1955-71; moved to syndication, where it ran until 1982)
* ''Series/PetticoatJunction'' (CBS, 1963-70)
* ''The Red Skelton Show'' (CBS, 1953-70; moved to NBC, ending in 1971)

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.
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