Starting from the Ancient World, with Ancient Greece etc., what dates would you set the periods to without overlapping each other. The problem I'm having with this is that various movements/revolutions seem to start while something else are still finishing up. Generally speaking there should be a viable cause (like the Crusades, the invention of the steam engine with the industrial revolution) or movement behind all of the dates. And the dates would extend all the way up until now, although applying periods to modern history is fairly black and white.
Which periods are important depend on what precisely you're trying to explain. If you're writing a political history of England, 410 matters as the date when the Roman legions left the island. But if you're writing an economic history of Britain, the final quarter of the fourth century is more important because that's when Britain's economy collapsed. If you're writing a religious history, the crucial date becomes c.600, when king Aethelberht converts to Christianity. History of migrations? 450, when the Anglo-Saxons appeared. I could keep going, but you can see the point - different dates matter for different kinds of historical discussions, and the dates we choose to define when periods begin and end are very contingent on the specific story we're trying to tell. All these dates I gave for England would be different if we were to ask the same questions in France during the same centuries.
This is why historians increasingly tend to allow the lines between different periods to blur. When you divide English history on either side of 1066 (when William the Conqueror overthrew the Anglo-Saxon king), you can easily miss the fact that the most important economic changes in England didn't start with William's conquest, but in fact began in the late 10th century. It took archaeologists decades to realize this, because most only studied the period before or after 1066. It was only when the barrier between these two periods was broken down, and archaeologists started examining evidence from both sides of the 'key' date, that they realized there was a very different story to tell between c. 950-1150.
And so it goes for any period of history. This is why historians today generally define their own period to focus on when they write a book, beginning where their story begins, and continuing until the time when the questions they're trying to explore are answered. This allows the questions to take center stage, rather than limiting our ability to understand the past to arbitrary starting / finishing dates.
I know this is a complicated answer to what should be a simple question; but that's how history usually works.
The problem is that all 'periods' are artificial. They are the tools used by historians to have general guideposts for when we look back on history. We use major events for their practical impact, but largely for their symbolic significance.
In most cases people living at the time had no idea that X or Y event or year would be known as a change of epoch.
Change takes years, decades or even centuries to be fully implemented, especially before recent events that mean that inventions can become commonplace across the globe within a year or two.