The Catholic Church plunged into a period of disorder and blindness (we might say) with Vatican Council II (1962 - 1965). The most insightful short answer, I must say, for this plunge, is that it exchanged CLEAR, SOUND, PRINCIPLES for PRINCIPLES WHICH ARE AMBIGUOUS, DEFECTIVE, AND HARMFUL.
What really happened, for one thing, is that the traditional language and terminology was discarded. It takes no rocket scientist to know this means trouble and confusion. But much more important is that the evidence very strongly supports the thesis of deliberate ambiguity and conspiracy against the Church. The Church, previous to Vatican II (1962-1965) had consistently declared that the writings and teachings of St. Thomas Aquinas, canonized about 1325, after over 300 miracles worked through him, were the LIGHT OF THE HOLY SPIRIT given to guide the Church until the end of time. The Vatican II Church has discarded St. Thomas Aquinas (for all practical purposes and not directly but by simply baptizing and exalting Vatican II and its documents). Now by St. Thomas I also mean all those writings and official documents which Rome and the popes have put forth, drawing upon the wisdom of St. Thomas. Now especially pertinent in this matter is the 100 years of papal encyclicals prior to Vatican II.
And so Rome now rules the Catholic Church based on the Authority of Vatican II and the Documents of Vatican II, and not upon traditional teachings and writings. And the Documents of Vatican II, once more are ambiguous, defective, erroneous - if not explicitly then implicitly and effectively - and very harmful to the Church in many ways.
Please go to http://vaticaniidebate.com/id6.html and read PRINCIPLES OF AND FOR ORDER; AND ST. THOMAS AQUINAS.