The Pharaohs, part 2
Looking back from the 20th century, we perhaps imagine ancient Egypt as being a stable political entity for all its existence.  This is not borne out by the facts, however - there were periods of serious crisis, times when the very existence of a united Egypt was seriously threatened.  These times are called "Intermediate periods", and occur periodically throughout the history of Egypt.

The First Intermediate Period

The first of these times of crisis happened after the end of the long reign of Pepi II.  As already hinted, his reign saw an increasing decentralisation of authority in Egypt.  When the central pillar of the system (the Pharaoh) was removed, the entire system collapsed.  The result was over 140 years of near anarchy, known to historians today as the First Intermediate Period.  It lasted from 2181BC to 2040BC, and records about it are very scarce.  Therefore, it is impossible to know how many Pharaohs there were, and even how many dynasties.  It has been conjectured that there were 4 different dynasties during this period (7, 8, 9 and 10), the first two of those lasting from 2181BC to 2160BC, and the latter two existing between 2160BC and 2040BC.  During the whole period, the capital of Egypt (in reality only upper Egypt) was based at Herakleopolis.

The Middle Kingdom

The Pharaohs of the Middle Kingdom came from Thebes, and initially ruled the southern half of Egypt until the country was re-united under Mentuhotep I (2060 - 2010) in around 2040BC.  However, it is useful to go back to the start of his dynasty to see his origins.  There were 2 dynasties during the Middle Kingdom:

The 11th Dynasty: 2134 - 1991 (3 Pharaohs)
The 12th Dynasty: 1991 - 1728 (8 Pharaohs)

And the Pharaohs were as follows:

The Second Intermediate Period

The strong rule of the Middle Kingdom did not collapse as quickly as that of the Old Kingdom.  There is, however, some evidence of a north-south split in the Pharaoh's authority, though not as pronounced as was once thought.  The documentary evidence for the 13th Dynasty is nevertheless patchy at best, though we can decipher 10 Pharaohs of the 13th Dynasty, which ruled between roughly 1782 and 1650:

Running concurrently with the last years of the 13th Dynasty, we also see an obscure 14th Dynasty ruling the Eastern region of the Nile Delta.  This was not the only house to set itself up in opposition to the "official" Pharaohs, however.  In the eastern desert and Delta regions, another dynasty was emerging, the 15th Dynasty (also knows as the Hyksos - desert princes).  However, we have no precise dates for the "Pharaohs" of this line.  The same goes for the ephemeral 16th Dynasty, almost certainly a line of minor kings who existed in the shadow of the Hyksos.  This just demonstrates the sort of political fragmentation that was possible when there was no strong central authority.

Thebes was producing another line of kings whilst the Hyskos consolidated their grip on the north of the country - here we see the emergence of the 17th Dynasty.  Although relations between this group and the Hyskos were initially peaceful, the situation deteriorated rapidly, leading to several major confrontations.  It is highly likely that one of the kings of the 17th Dynasty was killed in one of these battles, since his mummy shows that he died having suffered terrible head wounds in battle.  In the 1570sBC, a series of hard-fought campaign saw the Theban kings triumph over the Hyksos.  The Theban king established the 18th Dynasty and ushered in the New Kingdom.