Hi, hopefully we'll get a comprehensive overview, but we've had several threads on the Beatles, so I've trawled the sub for comments attempting to explain various aspects of their popularity:
Did the Beatles truly innovate music massively or are they just a glorified pop band? - /u/lukeweiss leads with "The Beatles are absolutely the vanguard of the seismic shift in recording standards that occurred in the 60's..."
I've been reading up on The Beatles a lot lately and Sgt Peppers seems like such a major shift. I've read that Pet Sounds influenced them to switch from albums with 1-2 singles then filler, to spending 6 months making the entire album with the intent of every song being a hit. How true is this? - /u/thesweetestpunch on albums being a "full artistic statement", example: Sgt Pepper
What factors lead to The Beatles pursuing Indian influence in their later years? How did this contribute to the emerging youth culture in England (and America)? - /u/DaveM191 discusses the additional hippy appeal of Indian influences
Today is the 50th anniversary of The Beatles playing Ed Sullivan, what was the marketing campaign like to ensure such a huge audience at home? - /u/bfg_foo talks about early marketing in the USA
With songs like Revolution and Back In The USSR, was the public reaction to the Beatles' White Album very controversial in America? What about in the UK? - /u/CosmoDanger touches on aspects that made the Beatles controversial (since controversy = publicity)
Was there ever any kickback in the US because of The Beatle's Back in the USSR? - /u/davratta mentions the "more popular than Jesus" controversy
Besides being groovy, how did the Beatles get so popular? - an old thread with a few more suggestions