I really want to learn more about Church history. Catholicism is so darn fascinating.
CASTI CONNUBII - ENCYCLICAL OF POPE PIUS XI ON CHRISTIAN MARRIAGE DECEMBER 31, 1930
Note that Pius XI states the perennial teaching of the Church which is the primary end of marriage is the procreation of children. Since Montini's encyclical on the same subject in 1966 does NOT state this, that immediately red flags it.
Deal only with official Church teaching from before 1958 - i.e. before Vatican-2. Below is a good compendium of papal encyclicals, apostolic constitutions, etc. If you have any particular area of interest, feel free to ask.