From Wikipedia

Egypt - Why The Old Kingdom Fell

The Fifth Dynasty began with Userkaf (2465–2458 BC), who initiated reforms that weakened the Pharaoh and central government.

Egypt's expanding interests in trade goods such as ebony, incense such as Myrrh and frankincense, gold, copper and other useful metals inspired the ancient Egyptians to build suitable ships for navigation of the open sea. They traded with Lebanon for cedar and traveled the length of the Red Sea to the Kingdom of Punt, which is modern day Ethiopia and Somalia for ebony, ivory and aromatic resins. Ship builders of that era did not use pegs (treenails) or metal fasteners, but relied on rope to keep their ships assembled. Planks and the superstructure were tightly tied and bound together.

After the reigns of Userkaf and Sahure, civil wars arose as the powerful nomarchs (regional governors) no longer belonged to the royal family. The worsening civil conflict undermined unity and energetic government and also caused famines. But regional autonomy and civil wars were not the only causes of this decline. The massive building projects of the Fourth Dynasty had exceeded the capacity of the treasury and populace and, therefore, weakened the Kingdom at its roots.

The final blow was a severe drought in the region that resulted in a drastic drop in precipitation between 2200 and 2150 BC, which in turn prevented the normal flooding of the Nile. The result was the collapse of the Old Kingdom followed by decades of famine and strife. An important inscription on the tomb of Ankhtifi, a nomarch during the early First Intermediate Period, describes the pitiful state of the country when famine stalked the land.