The 1st Intermediate Period came to an end in 2040 when 11th Dynasty king Mentuhotep II finally succeeded in overthrowing the Heracleopolitan kings of the 9th/10th Dynasty , thus reuniting Egypt after almost a century of chaos and civil war. Later generations would come to see Mentuhotep as the second founder of Egypt .

He and his successors launched a new building campaign throughout the country to build impressive monuments. Egypt once again became a prospering nation. There are, however, indications of dynastic problems. The last king of the 11th dynasty, Mentuhotep IV, was omitted from later king lists, which might indicate that he was considered an usurper.

His vizier, a man named Amenemhat, probably became the first king of the 12th Dynasty . It is not known with certainty how this Amenemhat came to power: maybe he ceased it, maybe he was named Mentuhotep IV?s successor, or maybe he just rose to the occasion. A stone plate found at El-Lisht shows the names of the two kings next to each other, hinting at the possibility of a co-regency. If indeed there was such a co-regency between Mentuhotep IV and Amenemhat I, then Amenemhat was intended as Mentuhotep's successor and the co-regency was meant to make sure that the transition of power would go uncontested. This principle would be continued throughout most of the 12th Dynasty as well.

Amenemhat I moved the administrative centre of the country from Thebes to a new city, Itj-tawi ("the one that takes the Two Lands"), located somewhere in or near the Fayum-oasis, while Memphis became the official capital again. Thebes would however gain importance, as it became the centre of the cult of Amun , a god of obscure origins, to whom the kings of the 12th Dynasty felt some special allegiance.

Amenemhat I and his successors continued the building policy of the kings of the late 11th Dynasty . This building activity was financed with the spoils coming from military campaigns in Nubia, where Amenemhat and his son Sesostris I regained control of the region South of the first cataract. Along the Eastern frontier and in Nubia fortresses were built to prevent nomad tribes from entering the country uncontrolled.

Sesostris III brought the 12th Dynasty to its political, economical and cultural climax. He too directed campaigns against Nubia, advancing the Southern border to the second cataract or beyond, where he would later be venerated as a god. Although Egypt did not show an interest in that region for a long time after Sesostris III , he waged the first military campaign against Syria-Palestine, most likely to punish some nomad raiders who had tried to enter the country.

He also made some very important changes in the administration of the country, thus eliminating the local governors who had still retained much of their power since the 1st Intermediate Period.

The rest of the 12th Dynasty was prosperous and peaceful. Sesostris III?s successors waged no more wars and his administrative reforms gave them the power to rule the country without the local governors.

Although the 13th Dynasty monarchs were generally weak and meaningless figures, true power in Egypt was in the hands of the central administration and some powerful families, thus securing the country's stability and prosperity.

There was almost no military activity of any significance and the fortresses along the Eastern border were either abandoned or they no longer functioned to keep the Asian nomads out of Egypt. Attracted by the wealth, the prosperity and the soft climate in Egypt, more and more Asian nomads passed the borders peacefully. And while the kings of the 13th Dynasty lay dormant in their palaces, the country was taken over by a group of Asians known as the Hyksos.

The table below lists the dynasties that were part of the Middle Kingdom: