History seems to have a fractal quality, where learning about one thing leads to a another thing, which leads to another thing, until you get to some chain of events, and at some point you get to a point where you are researching US tariff rates in the 1920’s [1] to see if that caused the WW2 war in the Pacific. The point is, in school we had to learn the three causes for this or the two factors for that, but when you take a look at it the fabric of history is woven by many threads, which on closer inspection, turn out to be their own fabric with their own threads, and its not so easy to make sense of it.
As a running log:
The Mongols were invading Europe, and while in Poland, with nothing standing in their way of sacking the entirety of Europe, their leader died (not in battle), and they turned around and returned to China.
At some point in the Mongol empire, the Khan decided to convert the entirety of the empire, from Poland to the Yellow Sea, to Christianity, and sent an envoy consisting of Marco Polo's father and uncle, to ask the Pope for one hundred missionaries. For unclear reasons the Pope decided not to take the offer, and sent just two low level monks who promptly deserted at the first opportunity.
General Grant was key to the Union winning the American Civil War, and was somehow plucked from destitution as a firewood salesman and later rose to leading the Union Army.
In the second Greek-Persian war, the Athenian’s naval fleet proved decisive. The fleet was financed by a chance discovery of a silver mind, of which the proceeds were solely directed to building a fleet. If the silver mine had not been discovered, then the Persians would have conquered Greece, and the entirety of Western Civilization would have been altered.
History has causal opacity.