Egypt's ancient history covers a huge block of time. Archaeologists noticed something very interesting. They realized that much Egypt's ancient history could be divided into three big blocks of time. In each block, all of the pharaohs behaved in a certain way. 

Scientists have named these blocks "The Old Kingdom", "The Middle Kingdom", and "The New Kingdom". 

The Old Kingdom (2700 BCE-2200 BCE): Pharaohs had absolute power and were considered gods on earth. But that's not why this kingdom is nicknamed "The Pyramid Age".  Pharaohs were buried in pyramids only during this time period in history. 

After building a few pyramids, at great expense to the state, it occurred to pharaohs that pyramids were rather easy to spot, and thus, much easier to rob than a hidden tomb.  Things changed during the middle kingdom.

The Middle Kingdom (2100 BCE-1800 BCE): The middle kingdom was Egypt's Golden Age. Trade flourished, arts and literature flourished. Egypt built strong armies to defend herself against her neighbors. During the time period of the middle kingdom, pharaohs were expected to be good kings and wise rulers. 

Instead of building huge expensive pyramids, when pharaohs died, they were buried in hidden tombs. These tombs were all over ancient Egypt. Most probably, there are tombs yet to be discovered by modern archaeologists because they were hidden so well. 

The New Kingdom (1500 BCE-1000 BCE): The new kingdom was Egypt's expansion period. Egypt expanded her borders through military conquest and became a world power. 

During the time period of the new kingdom, pharaohs were all powerful, and pharaohs were all buried in the same geographic area called the Valley of the Kings.

Egyptian Timeline (interactive) 

Timeline (story and activity)