Four Historical Points define this century.
Martin Luther
In 1507 a young man named Martin Luther (1483-1546) was ordained an Augustinian priest. Sometime after his ordination, Luther began to experience severe doubts and inner turmoil over his salvation. These doubts and turmoil led him to develop two doctrines that were directly opposed to the teachings of the Catholic Church. The first doctrine claimed that Scripture "alone" was the sole rule of faith while the second insisted that people were saved by "faith alone". On November 1st 1517, Luther made public his "famous" ninety-five thesis that questioned and challenged numerous teachings of the Catholic Church. What followed was the Revolt. It divided Christianity into two main religious bodies - Roman Catholicism and Protestantism. In 1521 Pope Leo X excommunicated Martin Luther.
St. Ignatius Loyola
In 1521 while defending a castle in Spain, a brave professional soldier named Ignatius Loyola (1491-1551) was wounded. While recovering from his wound, Ignatius had a conversion of heart. He put away his armor and sword and embraced the life of a pilgrim. Eventually he entered the university of Paris and began studying for the priesthood. In 1534 with several other men St. Ignatius founded the "Company of Jesus" and in 1537 he was ordained a priest. Through their preaching, teaching, missions and loyalty to the Pope, the company of Jesus, also known as the Jesuits, became a major force in reforming and defending the Church.
Council of Trent
The Church was not indifferent to the Protestant Revolt, but swiftly responded to it by convening the Council of Trent (1545-1563). Trent not only condemned the Revolt, but also re-confirmed the ancient teachings of the Church. While Pope Pius IV successfully brought the Council to a close, St. Pius V used the documents and teachings of the Council to reform certain abuses within the Church. Two of the most important developments to come out of the Council was a Universal Catechism, which explained the Catholic faith, and the development of a seminary system to train future priests.
The Church of England
King Henry VIII of England in 1534, through the "Act of Supremacy", made himself the head of the Church of England. What drove Henry to sever all ties with Rome was Pope Clement VII's refusal to grant him a divorce from his wife Catherine of Aragon. Since the Pope had already given Henry a dispensation to marry Catherine he refused to give him another one. Even though the Pope said "no" to Henry's request, Henry went ahead and married Anne Boleyn in 1533. Following his marriage to Anne Boleyn, Clement VII excommunicated Henry. Henry in turn responded by taking over the Catholic Church in England and becoming its head.
For further reading about topics discussed in this century, refer to the following:
Facts about Luther
By Msgr. Patrick F. O'Hare
Characters of the Reformation
By Hillaire Belloc
How the Reformation Happened
By Hilaire Belloc
A Pilgrim's Journey: The Autobiography of St. Ignatius of Loyola
By Joseph Tylenda, S.J.
Saint Ignatius Loyola
By FA Forbes
Saint Ignatius Loyola: The Pilgrim Years 1491-1538
By James Brodrick, SJ
The Spiritual Exercise of St. Ignatius Loyola
By: St. Ignatius Loyola
Catholicism and Fundamentalism: The Attack on "Romanism" by "Bible Christians"
By Karl Keating
Not by Faith Alone: A Biblical Study of the Catholic Doctrine of Justification
By Robert A. Sungenis
Not by Scripture Alone: A Catholic Critique of the Protestant Doctrine of Sola Scriptura
By Robert A. Sungenis
Nuts & Bolts: A Practical Guide for Explaining and Defending the Catholic Faith
By Tim Staples
What Catholics Really Believe-Setting the Record Straight: 52 Answers to Common Misconceptions About the Catholic Faith
By Karl Keating
Where Is That In the Bible?
By Patrick Madrid