Egypt was reunited at the end of the First Intermediate Period by Montuhotep II and entered a second substantial period of unity known to modern historians as the Middle Kingdom.
This period of history last around 300 years, and comprises the second half of the 11th Dynasty, the 12th Dynasty and the 13th Dynasty. It is a time of a great flowering of the arts and literature, and texts from this time were used to teach scribes to write during the later periods of Egyptian history (and so have been preserved for us).
Religion underwent changes which are sometimes referred to as a “democratisation of the afterlife” – the cult of Osiris and the idea of an afterlife for everyone (who could afford the necessary rituals and funerary practices) were key developments of this period.
Central authority once again dribbled away at the end of the period under similar circumstances to the end of the Old Kingdom. A long lived king, some ephemeral successors, poor harvests due to low flood levels (which casts doubt on the king’s legitimacy). The rise of rival rulers and autonomous cities in the north of the country begins the Second Intermediate Period.