What is the least known fact in history that you think more people should know?

The Tang Dynasty of China was on the brink of collapse in the mid 9th century, when a group of Buddhist monks invented gunpowder. At this point, the Tang Dynasty was already in its final stages and was eventually overthrown in 907 AD. During this time though, the invention of gunpowder spread throughout the world and would eventually become a crucial factor in the outcome of many battles.