In 1321, in response to Mamluk Sultan an-Nasir Muhammed persecuting the Coptic Christians in Egypt, Emperor Amda Seyon I of Ethiopia threatened to permanently destroy Egypt by redirecting the Nile.
Redirecting rivers to cause floods is a tactic that has been used throughout history, from the Qin flooding Wei's capital with water from the Yellow River in 225BC to Ukraine creating mud to force the Russians to use vulnerable roads in 2022. It also happened by accident when California created the Salton Sea in 1905. However, doing the opposite and redirecting a river to create drought and famine is not such a common tactic.
Let's imagine a scenario where Amda Seyon and an-Nasir Muhammed come to blows and the Ethiopian Emperor chooses to redirect the Nile.
Firstly, did Ethiopia have the technology to pull this off? While digging irrigation canals wasn't exactly new technology, redirecting a river is quite a bit larger in scope!
Secondly, where would be the easiest place to redirect the Nile to? North-West to the Sahara Desert (possibly flowing into the Qattara Depression)? East to the Red Sea? Or even draining Lake Tana South into the Awash River, leaving the White Nile (which only carries 10% of the Nile's water) untouched?
Finally, what would be the consequences of this abhorrent act of un-terraforming? Obviously, it would cause a severe humanitarian crisis in Egypt, and probably also all the states near Egypt as they get flooded with refugees (ironically including Ethiopia itself) but this still leaves the issue of long term effects such as ecological damage and the loss of the Mediterranean's biggest breadbasket and link to Sub-Saharan Africa.
