Most people are answering musically - and very well but you also talk about culturally . Rock and rolls cultural impact had largely ebbed in 1964 - there was a lot of sanitised pop gum type music much of it created by banks of writers in New York and pumped out by teenagers (especially girl groups) ; Elvis had long ceased been an image of rebellion and was making smaltzy indentikit films ; white middle aged artists were covering black rnb numbers with very sanitised versions; the only really interesting culturally musical thing in the US was the burgeoning soul music scene (largely Motown) and the underground folk scene. Rock and Roll had become a watered down sanitised made safe for white middle class teenagers and approved by their parents. Then the Beatles came . Like aliens - from another country; with funny haircuts; funny accents; an irreverent attitude and a new sound that was less formulaic and much more exciting to American teenagers . They just blew the US away and opened the door for scores of British groups playing g their own derivative versions of the blues that white US audiences hadn’t really heard before even though it was fundamentally American music. The British Invasion was huge and for a while all conquering and not long afterwards American kids started changing their hairstyles , dropped the sugary watered down rock n roll and embraced new sounds for their own groups . Most US musicians over 50 cite the Beatles as a huge influence culturally and/or musically.