The Nile is the sole reason for all life in Egypt's Nile Valley — every blade of grass, every tree, every animal and every person owes their existence to this river.
The narrator explains that Egypt's extreme aridity means the Nile is the only water source, making it the foundation of all life in the region for at least five thousand years.
transcript
Paul Cooper: Egypt itself has an extremely arid climate, and its inland territories experience virtually no rainfall. If geography had been only a little different and Lake Victoria had not begun to drain westwards, we can only imagine how differently history might have gone. For at least the last five thousand years, every blade of grass and every tree in the Nile Valley, every animal and every person to ever live, every priest and every king, owes their existence solely to this river.