Great question.

In the United States, on-screen violence wasn't the inspiration for time delays. Rather, time delays came about because of profanity, nudity and sexual content. Moreover, the widespread use of time delays is an extremely recent phenomenon, dating from within the past 15 years.

But let's take a step back before we put that modern use into context (we have a 20-year rule here to watch out for, after all).

"Live delay" or "time delay" has its origins in Federal Communications Commission rules on indecency. Under 18 U.S.C. § 1464, passed in 1948, the FCC has the authority to regulate the broadcast of obscene, indecent or profane material. Generally, the FCC defines this as "material that, in context, depicts or describes sexual or excretory activities or organs in terms patently offensive as measured by contemporary community standards for the broadcast medium."

There is, and never has been, a formal restriction on violence, and the FCC has a lengthy and tortuous history when it comes to meeting these 1948 guidelines. We'll come back to that history in a bit.

The same year that Congress gave the FCC powers to regulate obscene, indecent and profane material, radio broadcaster Jerry Williams began a noontime program at WKDN-AM in Philadelphia. Williams had pioneered a talk radio style that included a fair bit of audience interaction, and at WKDN, he invited listeners to call in and give their opinions on issues.

FCC privacy rules in place at the time mandated that only one side of a telephone call could be aired, so Williams repeated callers' comments with a comedic bent, reading them live onto the air.

Before arriving in Philadelphia, Williams worked at WKAP-AM in Allentown, Pennsylvania. Four years after Williams began his noontime show in the big city, WKAP began its own call-in show, but with a technological trick that Williams doesn't seem to have had. To get around the FCC's restrictions, WKAP had two tape machines set up. One machine recorded the incoming phone call, then its rollers spanned the tape to the second machine, which would play the recording over the air.

This process neatly sidestepped the FCC's restrictions on "live" telephone calls, and the resulting delay of a few seconds allowed engineers to catch callers' profanity before it made it on the air.

This history is relayed by Atlas Obscura's Eric Grundhauser, who also interviewed Joe Snelson, former president of the Society of Broadcast Engineers, who described a similar process for television:

"[When I started,] stations would place two video tape recorders side by side,' he says. 'The machine on the left would record the program on tape. The tape would exit the machine, go over a series of rollers and then go into the second machine on the right for playback. Since the tape ran at 15 inches per second you would need a distance of about about nine feet between the machine tape paths for a seven-second delay.' This allowed a crucial few seconds for editors, directors, or engineers to catch anything they deemed indecent before it hit the airwaves."

In addition to Ruby's assassination of Oswald, there is the notorious 1967 execution of a Viet Cong prisoner in front of an NBC TV camera, and the horrifyingly tragic live suicide of Christine Chubbuck in 1974.

These events did not spark a surge in the use of time delay. Again, it was sex, nudity and profanity that drove this adoption. Louis Chunovic's One Foot on the Floor: The Curious Evolution of Sex on Television from “I Love Lucy” to “South Park” is a good book to read, as is Michele Hilmes' Only Connect: A Cultural History of Broadcasting in the United States.

In 1950-1951, Congress held hearings on TV content after some viewers complained about the plunging necklines of some gowns worn on TV. As a result, broadcasters established a voluntary ethics code that led to things like "I Love Lucy" being forbidden from using the word "pregnant". Married couples were frequently depicted as sleeping in separate twin beds.

A 1957 incident in which Jayne Mansfield's breasts "accidentally" popped out of her gown during the Oscars telecast brought more complaints than the Oswald assassination did six years later.

In the 1970s and 1980s, the trend of voluntary censorship switched to one of legal censorship. The Supreme Court case FCC v. Pacifica, inspired by an airing of George Carlin's famed "Seven Words" monologue, resulted in the FCC's censorship powers being confirmed. In 1983, broadcasters abandoned their voluntary code of censorship after the U.S. Department of Justice indicated it could run afoul of antitrust laws.

In the late 1980s and early 1990s, national politicians began to criticize what they saw as a disrespect for traditional culture. One of the more famous remarks came in 1992 when Vice President Dan Quayle said that Murphy Brown's depiction of a woman having a baby out of wedlock disrespected "family values."

Shock radio, FOX becoming the fourth broadcast network, and more daring broadcast TV shows like NYPD Blue in turn encouraged clauses within the Telecommunications Act of 1996 that required TV shows to have content ratings and for TVs themselves to have content-limiting features.

Most of these moves addressed scripted broadcasts, however. The shift to address live TV didn't come until after 2000, in the period 2003-2004, when a series of high-profile events (including the infamous Super Bowl halftime show) forced broadcasters to adapt. The Oscars began using a time delay for the first time, as did the Golden Globes, even NASCAR races, out of fear that someone might do something daring.

With the national networks beginning to self-censor their live content on a wide scale, individual TV stations began doing the same as well. Sales of automatic software and hardware tools boomed, and both are now widespread, both because the cost has come down and because Congress has increased fines for even fleeting violations of the decency standards.