The 5.9 kiloyear event, one of the most intense aridification events during the Holocene, occurs around 3900 BCE, ending the Neolithic Subpluvial and probably initiates the most recent desiccation of the Sahara desert.

Thus, it also triggers worldwide migration to river valleys, e.g.

from central North Africa to the Nile valley, what eventually led to the emergence of the first complex, highly organized, state-level societies in the 4th millennium BCE.

It is associated with the last round of the Sahara pump theory.A model by Claussen et al.

(1999) suggested rapid desertification associated with vegetation atmosphere interactions following a cooling event (Bond event 4).

Bond et at.

(1997) identified a North Atlantic cooling episode 5,900 years ago from ice-rafted debris, as well as other such now called Bond events that indicate the existence of a quasiperiodic cycle of Atlantic cooling events, which occur approximately every 1500 years.

For some reason, all of the earlier of these arid events (including the 8.2 kiloyear event) were followed by recovery, as attested by the wealth of evidence of humid conditions in the Sahara between 10,000 and 6,000 BP.

However, it appears that the 5.9 kiloyear event was followed by a partial recovery at best, with accelerated desiccation in the millennium that followed.

For example, Cremaschi (1998) describes evidence of rapid aridification in Tadrart Acacus of southwestern Libya, in the form of increased aeolian erosion, sand incursions and the collapse of the roofs of rock shelters.

In the Middle East, the 5.9 kiloyear event leads to the abrupt end of the Ubaid period.

The 5.9 kiloyear event is also recorded as a cold event in the Erhai Lake (China) sediments.

Historically, the period of the 5.9 kiloyear event is associated with the increased violence noticed in both Egypt and throughout the Middle East, leading eventually to the Early Dynastic Period in both the First Dynasty of Egypt and Sumer.

James DeMeo and Steve Taylor suggest that this period is associated with the rise of patriarchy, institutionalized warfare, social stratification, abuse of children, the development of the human ego, separation from the body, the rise of anthropomorphic gods and the concept of linear historic time.