Gutenberg's Printing Press
Johannes Gutenberg combined movable metal type, oil-based ink, and a modified wine-press into a machine that could print books faster and far cheaper than any scribe could copy them. Within decades, ideas — soon including heresy and revolution — could spread across Europe beyond any authority's power to control. Within a generation, a German monk's local complaint about the Church would use it to split Christendom in half.
A new way to record or transmit information lowers the cost of copying ideas and reorders who holds knowledge and power.