Following the Council of Trent, Pope St Pius V, concerned with some innovations and improper accretions in the Order of the Mass in some areas, reviewed the Roman Missal. When he was finished, he declared that all priests of the Latin Church throughout the World must use the Roman Missal he prepared when they said Mass. They could not add a single word to it, or choose to leave a single word out, without his authority. Only those rites which had already been established for more than two centuries before the date he promulgated the new Missal were allowed to say Mass differently (eg, the Milanese Rite, the Dominican Rite).
And so the Mass changed very little for over 400 years. (Parts of it, such as the Kyrie and the Eucharistic Prayer have remained unchanged for well over 1,000 years!) A few Popes made minor changes to the Missal over time. The Holy Week liturgies were changed in the 1940s. And then, many thought it was sacrilege, Pope John XXIII added the name of St Joseph to the Canon of the Mass (the Eucharistic Prayer). For over 1,000 years, since it had been settled by Pope Gregory the Great, the Canon of the Mass had not been changed. It was considered the untouchable core of the Mass.
Over the last 100 years, there had been considerable momentum in the "Liturgical Movement" calling for reform of the Mass, the possibility, for example, of saying Mass in the local language of the people rather than Latin.
And, of course, the Mass was so very different from the way the Protestants worshipped God.
Then, Pope John XXIII (not content on adding the most chaste spouse of the Blessed Virgin Mary to the Canon) convened the Second Vatican Council. The Fathers discussing the Sacred Liturgy decreed that Latin must remain the language of the Mass and the Church, that Gregorian Chant must retain pride of place in Sacred Music. They said that any reforms that were necessary and could grow organically from the existing form which would allow for greater participation of the laity was to be encouraged. They said that only where the local Bishop considered there were sufficient pastoral reasons could part of the mass be said in the vernacular. There was no permission for Mass to be said with the priest's back to God rather than facing Him. There was no suggestion that communion could be given in the hand standing. There was no suggestion of almost all reference to the Sacrificial aspect of the Mass being downplayed or removed. There was no suggestion that most references to angels and saints and Heaven should be removed. (click here to read the relevant parts of Sacrosactum Concilium, the Vatican II Constitution on the Liturgy.)
After the close of the Council, Pope Paul VI set up a Consilium to prepare a new Mass, to "implement the desires of the Council". He called a number of Cardinals together to see the new Mass celebrated and to comment. Apparently, favourable comments did not abound. The focus of the Consilium was clearly to reform the Mass far beyond what the Council Fathers had intended or desired. Several Protestant theologians were observers at the Consilium, the intention being that they should be able to say of the new Mass that there was nothing offensive in it to them. The focus had shifted very clearly to reducing the differences between the Mass and Protestant worship so as not to be a barrier to ecumenism. With all respect to His Holiness, millions of Catholics have suffered in the last 30 years because of this approach, and few Protestants have gained.
The Holy Father promulgated the New Missal and declared that within a matter of practically a few months, no other Missal could be used without the Latin Church, not even those rites which Pope St Pius V had deemed sufficiently established to be retained. All other ways of saying Mass were banned.
Within a couple of years, the Cardinal Archbishop of Westminster in England had obtained permission from the Holy Father for any priest in England and Wales to celebrate Mass according to the Roman Missal of 1962 (the last revision of the missal before the Council). Archbishop Lefebvre of Switzerland was not prepared to accept this ban and established his Priestly Society of St Pius X, refusing to accept any of the changes brought about by Vatican II (even though as a participating bishop, he had voted for many of them, including the Constitution on the Liturgy).
At the commencement of his pontificate, Pope John Paul II sought information from bishops throughout the world on the situation of those who were "resisting" the liturgical reforms. As a result of these reports, the Holy Father, seeking to accommodate the concerns of Archbishop Lefebvre's followers and others who preferred the pre-conciliar Liturgy authorised an Indult in 1984 allowing a limited permission for the Tridentine Mass to be said. There were quite a few restrictions imposed, however (eg, the Masses could not be said in Parishes).
In 1988, the Vatican and Archbishop Lefebvre signed a Protocol that would see the Holy Father approving the appointment of a bishop of Lefebvre's choosing in return for Lefebvre and his followers accepting the Church's Magisterium and that Vatican II and the promulgation of the new Mass were part of it.
Archbishop Lefebvre signed it, but later reneged on the agreement and went ahead and consecrated three bishops illicitly. He, the bishops, any priests of the Society and any members of the faithful who formally adhered to their schism were swiftly excommunicated... and remain excommunicated. The Holy Father, however, issued a motu proprio Ecclesia Dei stating that the aspirations of those who were attached to former liturgical traditions were "legitimate" and that Bishops should be "generous" in allowing Tridentine Masses to be offered in their dioceses. He established a commission whose primary responsibility was to help the faithful to obtain Latin Masses in their dioceses and to facilitate the return to the Church of those who were now in schism.
And return some did... Several priests of the Society soon returned to the Church and at the urging and with the blessing of the Holy Father formed the Priestly Fraternity of St Peter, an order of priests with permission to administer the Sacraments solely according to the Missal of 1962.
Latin Masses are being celebrated in Cathedrals around the World again, even by Bishops and Cardinals, although not yet by the Holy Father himself. There are, however, still many dioceses where the Faithful cannot attend these masses or it is made very difficult for them to do so. Please God, these Bishops will soon be generous as the Holy Father has asked them to be.