It was the pop culture equivalent of the Big Bang, a televised moment that changed music for decades to come.

Fifty years ago Sunday, the Beatles made their U.S. live television debut on "The Ed Sullivan Show" as 73 million people tuned in, the largest audience in history at that time. The English band's appearance ignited American hysteria over the group and its music on a scale unmatched to this day.

In the shorthand of history, it appears to be a moment of spontaneous combustion. In reality it was the result of musical talent, managerial chutzpah and marketing genius.

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But at the time, not even John, Paul, George or Ringo were fully aware of what was to come.

"We were busy — it was crazy at home," drummer Ringo Starr, 73, said in a recent interview. "We thought we were just coming to do some TV show. We were like, 'We're going to America!' — that's all I could think, we're going to America where all the music I ever loved came from. That was the big news for me."

From early on, the Beatles' manager, Brian Epstein, was determined to break his band in America.

"His conviction in the Beatles' qualities was unshakable from the start," said Mark Lewisohn, author of a new biography "Tune In: The Beatles — All These Years, Vol. 1." "He believed ... that they would be the greatest."

But through most of 1963, even the band's label wasn't taking much notice. Executives at Capitol Records, the sister label of Britain's EMI-owned Parlophone Records, deemed their music unsuitable for American audiences and repeatedly declined to release soon-to-be Beatles' classics including "Love Me Do," "Please Please Me" and "She Loves You."

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"I would occasionally take an EMI record, English in particular, and release it in the United States with no success whatsoever," Capitol's then-president, Alan Livingston, says in historian Bruce Spizer's 2003 book, "The Beatles Are Coming! The Birth of Beatlemania in America." "There was just no interest in English artists here."

True enough. Cliff Richard was the biggest pop star in England before the Beatles came along, selling millions of records at home. The best he could do in the U.S. was No. 25 for his late-1963 version of the 1950s pop-R&B ballad "It's All in the Game."

What's more, lead guitarist George Harrison found no awareness of the band when he came to America in September 1963 to visit his sister, Starr said.

"He said, 'It's going to be tough,' " Starr recalled.

That would soon change, as Beatlemania took hold in England — and American news outlets began to take notice.

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On Oct. 6, 1963, the Los Angeles Times published a London Times story about what had erupted out of the seaport city of Liverpool. Reporter Derek Jewell presciently noted:

"One genuine novelty, however, may make the sociologists twitter," he wrote. "Their talk reveals them as very much part of that questing, confident, cool, sharp and unshockable stream which has come of the grammar schools in the last decade."

The Beatles' refreshing candor, energetic music and irreverence won them a spot performing for the royal family at the Royal Variety Show in London on Nov. 4. That high-profile gig helped boost their profile across the pond.

The Beatles' name came up in Sullivan's world as early as summer 1963, when the show's British talent scout, Peter Pritchard, took notice of the quartet's rising popularity and the intense fan reaction during their performances.