The Printing Press triggered the Protestant Reformation

When Johannes Gutenberg's movable-type press began producing books in Mainz around 1450, it made information far cheaper and faster to spread. Within 60 years of the press's invention, Martin Luther nailed his 95 Theses to a church door in 1517 — and within two weeks, printed copies had reached every corner of Europe. Without the press, Luther's ideas might have died at a local council. With it, they ignited a century of religious war and permanently fractured Western Christianity. Elizabeth Eisenstein's landmark study called the printing press the 'agent of change'.

Source: Eisenstein, The Printing Press as an Agent of Change (1979)