What was the main OTL event and/or time period which finally sealed that Europeans will ultimately conquer and spread their culture and way of life across the globe?
What was the latest POD when this could've been easily prevented?
It's not as easy as one might think it is, as one cannot simply compare continents to each other without regarding their strenghts and, in my humple opinion more important, issues. Europe was in different eras behind in different aspects, be it science or socio-economic affairs.
But I can't deny that Europe had many, many, many geographic advantages over other areas of the same size; complex river systems allowed for easy trade and the huge amount of resources, coal and iron in particular, allowed not only many products to be produced, but also gave rise to many wars and rivalries that in one way or another only gave more incentives to invest in science and power projection to gain an edge over the other.
And while Sub-Sahara Africa had to fight many geographic issues such as a marginal amount of navigable rivers, many East Asian nations, in particular China, grew increasingly more isolationist after the Mongol Storm which hindered cultural and scientific exchange between the nations of the world.
A PoD to stop all this is hard to give, not because it's impossible, but rather because "domination" is quite hard to define in terms of geopolitics. But in my view, the "easiest" PoD to destroy European hegemony over large swaths of the world is either to change its geography which is by definition ASB, or to
- Keep strong and huge states like France, Russia and the UK from forming by fragmenting them. Less manpower and less resources mean less influence on areas outside of Europe. Requires an early PoD before the 1000s, I suppose.
- Buff Europe's neighbours. Have the Turkic people like the Kipchaks or Khazars coalesce into larger nations with more authority given to a high king. Stop tribalism. Let the Mediterranean be a sea contested between Christians and Muslims. Give the natives of the New World immunity to the various diseases brought by Europeans by allowing them to get into contact with them prior to any serious European colonization endeavors. Etc.
- Stop absolutism and imperialism. Pretty self-explanatory.
I think it's possible to write a TL where all of these things happen. The (Western) European nations were very, very, very lucky in terms of geography and some events that just so happened to lead them to the right path. I'm sure you can butterfly at least the latter away.