What event marks the beginning of the modern world? The Renaissance? The Enlightenment? Or the French Revolution? Why?
Arguably, the Renaissance was the precursor for the events that you mention, in addition to the Protestant Reformation. Therefore, we could say that the Renaissance marks the beginning of modernity.
The Renaissance, culturally, is characterized by the emergence of humanism -- that is, a current of thought that places Man, or humanity, at the center, eschewing the supernatural as well as the supreme influence of the Church. Whereas Christianity taught us that human beings are innately sinful, humanists put forth the idea that we are inherently good and decent and that rational thought -- not salvation -- would provide the solution to our problems.
The Renaissance, which means "rebirth" in French, elevated Classical ideals of beauty and touted the importance of education. Literature did not go away during the Middle Ages -- stories were, in fact, very important to courtly life and, during the early 14th-century, "The Canterbury Tales" became the first Romance that was accessible to middle-class audiences. However, literacy became more widespread during the Renaissance after the invention of Johannes Gutenberg's printing press around 1440. (Note: There is Western bias here. The earliest document printed by movable type is the Jikji, an anthology of Zen teachings, printed in 1377. This evidence shows that the first printing press was, in fact, invented in Korea. However, the Korean press was rudimentary. Gutenberg's press was more technologically advanced, employing a matrix and hand mold, allowing for simpler and faster production).
Politically, more modern ideas of leadership also emerged. Niccolo Macchiavelli's "The Prince" encouraged the idea that a savvy political leader would prefer to be feared over being loved. He used the powerful Medici family as his model. In England, during the latter part of the Renaissance in the mid-16th century, Henry VIII appropriated the Protestant Reformation for his own selfish purposes and disavowed Catholicism, thereby declaring himself head of the Church of England, which led to the creation of Anglicanism.
Thus, the Renaissance is key to the emergence of modernity for three reasons: firstly, its daring proposition that faith in humanity is more important than faith in God; secondly, the invention of Gutenberg's printing press, which made it easier to share and spread information; thirdly, its dismantling of the supreme power of the Catholic Church in favor of a form of Christian faith which encouraged a more direct communication with God and personal access to Scripture.
These three events were revolutionary and, without them, the Enlightenment, which further questioned the infallibility of the Church and relied very much on print to spread ideas, would not have happened. Nor would the Scientific Revolution which preceded it. Finally, it was Enlightenment ideas which contributed to both the American and French Revolutions. One could, thus, view modernity as a time line which begins with the Renaissance and continues to our present day.