Why is Egypt called the 'Gift of Nile'?

The Egyptian Civilization emerged in the valley of river Nile and flourished for more than 2000 years. The river Nile has proved to be such a great boon for Egypt that the Greek historian, Herodotus called Egypt, "the Gift of Nile." If the river Nile would not have been there, Egypt would have been a part of the vast Sahara desert.