The 50's saw the exciting birth of Rock 'N Roll. After a few great years, by 1963 it had hit a lull. Elvis was in the military, Chuck Berry was in jail or something. Rock listeners were forced to endure hits by the likes of Fabian, Pat Boone, and Frankie Avalon. The country was in mourning after the JFK assassination.
That's the context of when the Beatles came along in the U.S. They were a charismatic bunch, and their early hits were full of excitement, and it was a new sound. The early songs were more complex than they sound, and more advanced than a lot of the other groups of the time. And they paved the way for all the groups that followed.
Or so I have read.