How might history be different if one of these events hadn't happened

One way to understand what History is, is saying that it is a probabilistic science. Historians are always, even when they are not explicit about it, working with an "alternative history" in their minds, i. e., they are always asking themselves "what would have happened if ... ?".

That means when a historian is explaining what happened and why it happened that particular way, he/she is choosing one specific thing to be that one if it had been different, the result would be other.

For example, many historians argue the killing of prince Ferdinando I was only an excuse for the starting of a war that was already in the making for a few years. They are saying that if Ferdinando I had not been killed something else would have started World War I. The high probability of this war was already given by the tense correlation of forces between European countries in the early 20th century. Had not Ferdinando I been killed, History would still happen as it did.

If you want to know how History would be different without a certain event taking place, you should pay close attention to the historical context of the event and the direct cause of it. With this in mind, you'll be able to tell if History would have been different or not.