Interesting - I was waiting for someone to bring up the Byzantines. I always wondered what would have happened if Constantine XI had a couple machine guns or even a good sniper with rifle in 1483.
The Turks would have been finished and the M.E. would be a very different place today.
How about if the Hungarian canon maker who sold artillery to the Turks had been more interested in helping Christians than in making a profit, and the big guns had been pointing the other way?
Of course that could have played out for good — the city is saved, the next push by the Muslims, either the West or the Rus come to the aid of Constantinople in the ensuing war Islam is pushed back into Arabia or even eradicated — or for ill — the next siege, a generation and a half later, succeeds, and when the Turks push into Romania, Vlad the Impaler is long dead, they meet no effective resistance and overrun Europe.
May 29, 1453. A Tuesday if I rememeber aright.