What follows is not intended to be an exhaustive analysis of Catholic and Reformation views of Mary, the mother of our Lord Jesus Christ.  However, it attempts to illustrate a timeline and cautiousness of beliefs, particularly in the papacy, about her role.  (Pictured at left is Our Lady of the Way, the Madonna della Strada.  She is the patron saint of the Jesuits.)
The Catholic Church
Popular views like the Assumption and the Immaculate Conceptiondeveloped into Papal teaching over time. In 1674 Pope Clement X (1670–1676) indexed books on Marian piety.[2] After the Council of Trent, Marian fraternities were founded, fostering Marian piety [3], some of which were outlawed by Popes. Not all Popes viewed Marian belief identically. Louis de Montfort was condemned in a Papal bull by Pope Clement X only to be praised by Pope Clement XI, canonized by Pope Pius XII and adored byPope John Paul II.
431: The Council of Ephesus approves devotion to Mary as the ‘mother of God’.
1265-1268: Pope Clement IV composes poem about the seven joys of Mary.
1603: Pope Clement VIII’s papal bull Domenici Gregis condemns negations of Mary.  His papacy supports the creation of Marian congregations and praying the Rosary.
1673: Pope Clement X issues a papal bull condemning the type of Marian piety which Louis de Montfort would later embrace and outlaws certain Marian devotions.  However, other bulls encouraged the recitation of the Rosary.
1712: Pope Clement XI instructs the Holy Office not to persecute anyone using the words ‘Immaculate Conception’ when referring to Mary.  He lays the groundwork for — although does not institute — the dogma of the Immaculate Conception.  He establishes the Feast of the Immaculate Conception for the whole Catholic Church.  He advocates the Marian teachings and devotions of Louis de Montfort (1673-1716).
1748: Pope Benedict XIV expands indulgences connected with praying the Rosary and furthered the congregations dedicated to the Sodality of Our Lady.
1769-1775: Pope Clement XIV decreed that only the Franciscans in Palermo could celebrate the feast of the Immaculate Conception.  This came after much popular unrest in the south of Italy surrounding the feast.  He later granted permission to other orders for private Masses only on this feast.  Interestingly, it is said that he pledged to dogmatise the Immaculate Conception, however, this did not happen.
1848: Pope Pius IX, bowing to popular clamour, appoints a theological commission to study a possible dogma around the Immaculate Conception.  He issues an encyclical, Ubi Primum, in which he asks for his bishops’ views on the Immaculate Conception.
1852: Pius IX appoints a commission of theologians to draft the dogma of the Immaculate Conception.  Later that year, he asks a group of selected cardinals to finalise the text.
1854: Pius IX declares the dogma of the Immaculate Conception.  He opposes petitions that this dogma be included in the creeds.
1869-1870: Pius IX opposes moves for a dogma of the Assumption (Mary’s physical ascent into Heaven upon her death).  Yet, he believed that Mary was a Mediatrix of salvation, as stated in Ubi Primum.
1878-1903: Pope Leo XIII issues a record 11 encyclicals concerning the Rosary.  He institutes the Feast of the Queen of the Holy Rosary.  He beatifies Louis de Montfort, referring to his Marian teachings, saying that a revival of the Catholic faith (weakening because of Modernism) would not be possible without Mary’s help.  He writes that Mary is Mediatrix and co-Redemptrix and is the first pope to fully embrace her role as Mediatrix.  He says that she administers all graces on Earth.  He relies on the writings of Thomas Aquinas in his justification of Mary as co-Redemptrix and mother of Christians everywhere.  Where the Church verified Marian apparitions, Leo XIII supported veneration at those sites.
1903-1914: Pius X affirms that Mary is the spiritual mother of all Christians.
1914-1922: Pope Benedict XV has a strong devotion to Mary and placed the world under her protection during the Great War (WWI).  Among other things,he promoted Louis de Montfort’s Marian devotions during the month of May.
1922-1939: Pope Pius XI engages in discussions about a dogma of the Assumption.  He often quotes Bernard de Clairvaux, who said that we have everything spiritual we need in Mary.
1944: Pope Pius XII declares the universal feast of the Immaculate Heart of Mary.
1947: Pius XII canonises Louis de Montfort.
1950: Pius XII announces the dogma of the Assumption.  He leaves the Mediatrix question open.
1962-1965: The Second Vatican Council declares Mary the Mother of the Church.
1965: Pope Paul VI writes in his encyclical Mense Maio that Mary is the pathway to Christ.  Anyone who follows her will encounter Him.
1974: Paul VI promotes Marian devotions and declares that she is the mother of graces and has a special role to play in redemption.
1987: Pope John Paul II affirms Mary as the Mother of the Church in his encyclical Redemptoris Mater.
1997: John Paul II, addressing a public audience, re-emphasises Mary’s role.
Redemptoris Mater reads in part:
The Church teaches that Mary appeared on the horizon of salvation history before Christ. [57]
If the greeting and the name “full of grace” say all this, in the context of the angel’s announcement they refer first of all to the election of Mary as Mother of the Son of God. But at the same time the “fullness of grace” indicates all the supernatural munificence from which Mary benefits by being chosen and destined to be the Mother of Christ. If this election is fundamental for the accomplishment of God’s salvific designs for humanity, and if the eternal choice in Christ and the vocation to the dignity of adopted children is the destiny of everyone, then the election of Mary is wholly exceptional and unique. Hence also the singularity and uniqueness of her place in the mystery of Christ. [58]
2002: John Paul II publishes his apostolic letter, Rosarium Virginis Mariae, which cites St Louis de Montfort’s God Alone:
Our entire perfection consists in being conformed, united and consecrated to Jesus Christ. Hence the most perfect of all devotions is undoubtedly that which conforms, unites and consecrates us most perfectly to Jesus Christ.
Now, since Mary is of all creatures the one most conformed to Jesus Christ, it follows that among all devotions that which most consecrates and conforms a soul to our Lord is devotion to Mary, his Holy Mother, and that the more a soul is consecrated to her the more will it be consecrated to Jesus Christ.[59]
I have highlighted dates concerning St Louis de Montfort to show how certain perspectives can be in out of favour depending on popes or social movements at the time.  More importantly, it is worth noting how long it actually takes for a new dogma to be instituted.
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GJ - I omitted the part copied from the LCMS website, because I thought it was too mixed around to clarify matters. That was not Churchmouse's fault, but Missouri's. The LCMS cannot get justification by faith right, so we can hardly expect them to deal with lesser matters.
The early Luther still preached on the Assumption of Mary, but his later sermons declared she was a sinner. The Medieval exaggerations had Mary without any actual sin (Immaculate Conception of Mary - try to get that right, Lutherans) and rising into heaven (the Assumption).
Conservative Lutherans have agreed in the past that Mary never had children after Jesus (perpetual virginity) but that is a historical opinion and not a Biblical doctrine. 
Obsession with Mary grew after 400 AD and transported newly invented opinions and events back to Biblical times. Many fables grew up about Mary and still exist in traditional Roman Catholic literature.
Pope John Paul II increased the emphasis upon Mary during his pontificate.