Most of us, I think, tend to see Vatican II as the watershed event with respect to liturgical developments since the 1960s, and there is no doubt that the changes set in motion during and after the Council have had a momentous impact on the quotidian lives of Catholics, the way they understand and live their faith as well as the way they worship.
The revolutionary changes that rocked the Catholic world came as a shocking upheaval to many. Fifty distinguished celebrities, scholars, historians, artists and writers, including the famed novelist Agatha Christie, signed a 1971 petition to Pope Paul VI to preserve the old Mass, whose "magnificent Latin text, has ... inspired a hosto of priceless achievements in the arts ... by poets, philosophers, musicians, architects, painters and sculptors in all countries and epochs." Whether it was because Paul VI like Christie or not, the petition was met with some limited success, in what came to be known as the "Agatha Christie Indult." (Source)
Yet anyone who has delved more deeply into the sources of the revolutionary changes of the 1960s and '70s will know that while the proximate causes of the changes may be found in Vatican II and the liturgical innovations that flooded the Church in its wake, the principal causes of these changes lie much earlier, far back in the reforms of the Pian pontificates and even somewhat before.
A convenient brief summary of some of those pre-Vatican II influences may be found in a recent post by a Thomas Aquinas College student under the moniker of Maestro, "Vatican II and the Origins of the Liturgical Reform" (January 9, 2015). The author also references a number of much more detailed posts on the subject over at the New Hampshire blog by the unabashed name of "The Rad Trad."
Readers, especially those to whom the subject is new, will find a good beginning here. There is, of course, much, much more to be read and digested.
[Hat tip to L.S.]