the beatles broke up in 1966 and sgt pepper was their funeral: the truth behind the beatles only concept album, a thread.

in the summer of 1966 the beatles ended their touring career. each band member spoke openly about their unhappiness with touring; complaining about crowds, sound quality, and high physical demands on them. this ultimately lead to a stunt in their individual growth as musicians

sgt pepper isnt about creating a new band at all, it is about reviving an old one

paul loves the beatles more than anyone else on the planet. he will do anything to keep them together, to keep them writing music. thats why he wanted to do magical mystery tour, thats why he did the let it be doc, thats why he did sgt pepper.

after their final show in august the beatles immediately began pursuing other interests outside of the group. john flew to germany to film how i won the war, george went to india, and ringo and paul began spending time in new social circles

paul's decision to compose for the film independently upset john. john had always been insecure about his music around paul, for example his very public negative criticism of paul's yesterday. john had a tendency to feel left out an jealous when paul worked separately from him

other things occurring during this time:
-brian fell into a depression & struggled with drugs, his relationship changed with the boys, especially john & paul
-john & geroge began using experimental drugs while paul didnt
-paul began spending time with new art friends in london

i believe that all these factors created a domino effect that lead the to beginning of the beatles deterioration and ultimately break up. it was obviously their individual interests began separating them from each other and they were becoming tired of the group in general.

if you look at the song tracks on sgt pepper the underlying them for basically all of them is: youth.
- when im 64: a song paul wrote when he was 15
-lucy in the sky: where john altered his voice to sound younger
-im leaving home: a coming of age theme
-mr kite: the circus

sgt pepper was about their childhood.
this theme is most prominent in the sgt pepper singles: strawberry fields and penny lane. both songs are literally about their childhood in liverpool. john and paul reminiscing about better times.

this began the first time since the band formed that each beatle was involved in separate individual projects unrelated to the beatles. the beatles hiatus was so strange and lengthy that brian epstein had to hold press conference to deny the band had broken up