Paper

Once I think of paper, I consider the most serious military defeat in the history of China the Battle of Talas.

For those who have not heard of this happening, here is some background. It was the transition period between pre- and post-Islam dysnasties of Iran in the middle Asia, and the peak of Tang Dynasty in China - under the reign of Li Longji (李隆基, 唐玄宗). In short, the two empire ended up having a battle (for various possible reasons, including competing for the support amongst tribes of the middle Asia) near Talas. The Tang army was defeated; the empire was soon followed by the rebellion of An Lushan (安史之亂). The rest, alas, as they say, has become the history.

I said it was the worst miliary defeat not because 30000 Chinese soldiers were killed, or that the influence in middle Asia vanished quickly. More seriously, prisoners of war from the Tang empire transmitted their technology of making paper to their Islamic masters, and later to the Europe via the First Crusade. Without all these happenings, the world would be very much different from that nowadays.

PS. It is real fun to read the accounts from the two sides of the Battle - you can hardly believe they are describing the same event. The invented tale of Ryūnosuke Akutagawa (芥川龍之介) - In a Grove (竹藪中) - is a second best way behind.