Gunpowder was known in China from the 5th century, and was weaponised some time in the 9th. In OTL the Mongols introduced it to the Middle East around 1250, and it spread to Europe by 1350, causing the end of knights and huge castle walls.
If it was introduced (perhaps by a defecting Chinese person who decides to travel west) to Europe some time around 850-1000, how would tactics in Europe evolve? Is it possible that medieval sieges could still occur to some extent (maybe with Star Fort-type walls instead of rectangular)? What about the roles of cavalry and infantry. I can see infantry being kept as a second-line thing (Pike and Shot tactic), but would cavalry be abolished (easy to shoot horse?) or be expanded (easy to not get shot when moving faster?)
Although the main point of this thread won't be what exact conflicts would occur, I imagine some of you will decide to put them up anyway. So I'll answer the most likely question. The Islamic world gets the gunpowder as well, but about 50-100 years after Europe.
- BNC