How did the Nile river give coherence to ancient Egyptian society in culture economy and politics?

If you look at the Nile River system you find an area fed water through a giant desert.

Slow flowing water means easy transport for Ancient People of goods.

The large area of fertile land fed water by the Nile system means food and wealth.

A king or Pharo in this case controling this area with uncrossable desert all around means a single culture and coherant government.