Why do historians divide egypt's long history into different periods?

Question

For example old kingdom middle kingdom ptolemaic period etc

Answer 1

because it is VERY LONG indeed...

no seriously... the different periods are very much different from each other... just because they had a stable society didnt make the time stand still in ancient egypt... things changed over time... fashions, rites, laws, even the gods they worshipped... they were in many ways completely different kingdoms that happened to be in the same place just one after the other.

Answer 2

Because every period had different characteristics that remarkably distinguish it from other periods.
For example the Old Kingdom was known by pyramid building but the Middle Kingdom was known by exquisite subterranean Luxor tombs.
The Ptolemies were not Egyptian and they did not speak the native language as their mother tongue and they come as one dynasty, so they should be a separate entity when considered from the historic point of view. So it was easy and clear to divide the Egypt history. The only difficult separating line though was the transition from Roman to Byzantine era, which is a rather general or regional debate.

Answer 3

You might be able to figure out your own answer to your question if you look at what happened in the periods you listed. Look especially at the rulers and the type of government. Look up who Ptolemy was.
History, and other subjects, are often divided into periods because near the end of one period and sliding into the next period there are big changes of one kind or another. It's a way to organize and remember important matters.

Answer 4

BC, before christ, and AD after he was either born or died... yes, religious, i know... :P but its what scientists use... ie. egypt was in 2000 bc... etc.