But in addition to their sound, musical historians also say their timing was part of what allowed the Beatles to break through. "The Beatles were an incredibly lucky band," says Gordon Thompson, author of "Please Please Me: Sixties British Pop, Inside Out" and a professor at Skidmore College in Saratoga Springs, N.Y., where he teaches a course about the Beatles.
Many see the Beatles as the light at the end of a dark tunnel in American history – they arrived here months after the November 1963 assassination of President John F. Kennedy, the Cuban Missile Crisis and global tensions over the Berlin Wall – but their American debut was actually interrupted by JFK's death, which happened on the same day as the release of their second U.K. album, "With The Beatles." American television networks had planned to broadcast the news of the record release on their evening programs, only to postpone the segments in favor of the marathon coverage that followed Kennedy's assassination.
"For Americans at that point in time there was one crisis after another," Thompson says. "This is the era of kids routinely doing drills about how to survive a nuclear blast." But those same kids, members of the Baby Boom generation, were coming into their teenage years just as the Beatles looked to conquer their ears – and their wallets.
Also working to the Beatles' advantage was the rise of television, with the crises of 1963 cementing its place in American households. "Television becomes the place where everybody turns to see what is going on. It is the oracle in the living room," Thompson says.
The Beatles' Feb. 9, 1964, performance on "The Ed Sullivan Show" set TV records. An estimated 73 million Americans tuned in to their premiere performance, which played in 45 percent of homes with televisions in America at the time. They would play "Ed Sullivan" again at the end of their February tour and return for another series of stateside concerts in August. They would sell more than a million copies of each of their nine U.S. singles and six LPs, adding up to 25 million Beatles records sold in total in America that year alone.
It wasn't just their music that made the Beatles so appealing, It was the way they carried themselves, from their mop-top hair cuts and clean-cut suits to the way they interacted with the media. They blended a smart-alecky intelligence with a playful rebellious streak that was present from their very first press conference at the JFK airport. The British accents didn't hurt, either.
"They showed up in the United States and the stereotype of the rock 'n' roller had been Elvis Presley, who you could write funny articles about what a hick he was. And suddenly there were a bunch of British rock musicians who made American critics feel like hicks," Wald says. "They were amazingly articulate, and smart, and clearly thought they were smarter than the people writing about them."
Once the Beatles proved there was an American appetite for British bands, a number of U.K, acts -- including The Rolling Stones, The Animals, Donovan, The Who and The Yardbirds -- followed them across the Atlantic in what would come to be known as The British Invasion. Even American bands started trying to become more British, like the Sir Douglas Quintet, a San Antonio, Texas, guitar group that embraced a decidedly British-sounding name.
But the Beatles' influence went far deeper than just a band's name or country of origin. "It was very important that the Beatles wrote their own songs," says Richie Unterberger, author of "The Unreleased Beatles" and a number of other books about music history. "Even if young kids listening to them didn't realize Paul and John wrote most of their songs at that point, they could tell instinctively."
While plenty of other acts – including many of the African American musicians the Beatles idolized – had written their own music, most pop bands at the time did not. The Lennon-McCartney writing duo added an aura of authenticity that made their rivals, like Frankie Avalon, feel fabricated. Furthermore, the Beatles became known for their willingness to experiment and lead their efforts in the recording studio, an approach that "became much more accepted within the music industry, not just within record companies but within rock groups forming," Unterberger says.
Corrected on : Corrected, 1/24/14: : A previous version of this article misquoted Elijah Wald on the meaning of the Beatle’s success in America. He said, “Every British rock ‘n’ roll band before the Beatles had been considered just a simulacrum of American music.” The article also misidentified Gordon Thompson. He is a professor at Skidmore College.