why would it be important for a pharoh to unite upper egypt and lower egypt

Answer 1

Isn't a king or pharaoh more important if he rules a large country? By uniting the two, the pharaoh was able to control the Nile River.

Answer 2

are you sure?

Answer 3

If you look at the geography of ancient Egypt, you'll clearly see that it's in the pharoah's best interest to have the people of the upper Nile (to the south) and the lower Nile (to the north, where it flows into the Mediterranean Sea) under one rule -- for protection, for transport of goods, etc.
http://carbon.cudenver.edu/stc-link/AE/geography.html

Answer 4

Yes, I'm sure.

Check this site for more information.

http://www.historyworld.net/wrldhis/PlainTextHistories.asp?historyid=aa28