There's this fascinating BBC series for example, which looks at the history of the greatest human endeavor that is science, in a way that is different from the commonly spread notion that the evolution of science is all about geniuses having sudden eureka moments. Instead, it argues that there are complex factors piling up over large periods of time, and when a Galileo or a Newton inevitably appears on the scene, this is more like an end product of all those processes. In other words, when "the time is ripe" for something to happen, it will happen eventually.
On the other hand, I'm sure we could think of many events that didn't happen, even though the processes and factors were there. It's just that, maybe, the right person never appeared at the right place and time?
Anyway. It's a broad topic, so let's boil it down to the following question:
Imagine one of these influential persons of history were never born. The absence of which of them would've affected history in the most profound way?
Never born: which of these absentees would've diverted history the most? (part 1: religion & philosophy)
Never born: which of these absentees would've diverted history the most? (part 2: science & discovery)
Never born: which of these absentees would've diverted history the most? (part 3: politics & state)