Answer:
Why: A record setting 73 million people tuned in that evening making it one of the seminal moments in television history. Nearly fifty years later, people still remember exactly where they were the night The Beatles stepped onto Ed Sullivan's stage.
Circumstances: For several weeks American radio stations had been saturating the airwaves with Beatles music. The power of radio had led to sales of millions of Beatles singles and albums. For weeks, the country had been warned "The Beatles Are Coming!" The American press picked up on the story, with several magazines and newspapers running feature stories on the group. Two days earlier, CBS and ABC showed film of The Beatles' arrival in America at New York's Kennedy Airport on their evening news shows. But the big event was The Beatles' first live appearance on American television, which took place on the country's most popular variety program, "The Ed Sullivan Show"
Happen again: It might if there is another group as popular as the beatles and the expectative marketing campaign is as succesfull.
Step-by-step explanation: