Like any band, the Beatles' recording career was often altered, even pushed forward, as much by external factors as their own creative impulses. The group's competitive drive had them, at times, working to match or best Bob Dylan or Brian Wilson; their drug use greatly colored the musical outlook of John Lennon and George Harrison in particular; and the death of former manager Brian Epstein ushered in a period of distracting and poor business choices and opened the door for individuals such as the celebrity guru Maharishi Mahesh Yogi, Yoko Ono, and businessman Allen Klein to penetrate, alter, and, some would say, disintegrate their inner circle.
The most important of these external shifts in the Beatles narrative, however, was a series of changes that allowed them to morph into a studio band. The chain of events that ushered in the band's changing approach to studio music began before Rubber Soul, but the results didn't come into full fruition until Revolver, a 35-minute LP that took 300 hours of studio time to create-- roughly three times the amount allotted to Rubber Soul, and an astronomical amount for a record in 1966.
Longtime Beatles producer George Martin, justifiably upset that EMI refused to give him a raise on the back of his extraordinarily profitable work with the Beatles, quit his post with the label in August 1965. Martin used his clout to create his own company, and the group and producer used theirs to effectively camp out at Abbey Road Studios for whatever length of time suited them rather than being forced to comply to the rigid and economically sound schedules demanded by labels at the time. The Beatles could now work both in and out of the studio, taking full advantage of new advancements in sound recording that allowed them to reflect upon and tinker with their work, explore new instruments and studio trickery, and refine their music by solving problems when they arose.
This new approach not only greatly altered their work environment, but drove the Beatles to value the flexibility of emerging technology. They also cashed in some of their commercial capital to abandon the mentally and physically sapping practice of touring-- and the glad-handing and public relations requirements that went with it. Exceptionalism became the watchword for the band, and it responded by using its freedom to push forward its art and, by extension, the whole of pop music. Musically, then, the Beatles began to craft dense, experimental works; lyrically, they matched that ambition, maturing pop from the stuff of teen dreams to a more serious pursuit that actively reflected and shaped the times in which its creators lived.