Answer:
The geographic feature that made possible the union of Upper and Lower Egypt was the Nile river.
Step-by-step explanation:
Ancient Egypt was divided into Upper and Lower Egypt prior to its unification. Both lands were separated by the Nile: Lower Egypt lied north where the Nile stretched out forming the Nile Delta; and Upper Egypt was to the south.
The terminology Upper and Lower makes reference to the flow of the Nile from the higlands of East Africa towards the Mediterranean Sea to the north.