I'm sure everyone remembers the Nintendo Dream Interview about Three Houses few years ago following the release of Cindered Shadows, bringing an end to the DLC of Three Houses. The interview revealed a bunch of interesting stuff like Claude's real name, but most relevant to this post is the discussion of why Nemesis attacked Zanado, specifically the mention of the nabataen's governance of the land following Sothis beginning her slumber after healing the world.

There is a school of thought, popular amongst Edelgard apologists especially in the Edelgard discord server that is known for being a haven for genocide apologists and the like, which is that the nabataens were oppressive tyrants, whose actions completely justified their genocide at the hands of the so called King of Liberation. Now before we can truly get into things, we need to understand what was said in the interview which has two main translations from what I gather, with the first from Serene's Forest being;

In that world, originally the race that could change into dragons, the so called citizens of Nabatea, were scattered about Fodlan in the different places/lands as governers (rulers) 

And the second from NintendoEverything and a translation done by dubstepkazoo which can also be found here is;

In that world, the Nabateans were a race of people who could transform into dragons, and ruled as gods over each territory across Fódlan.

Now then, neither of these translations don't appear to explicitly support the narrative that the nabataens were cruel and oppressive tyrants, with the closest being the second translation which says they ruled as gods, which by itself merely means they were worshipped by the people.

Additionally, there are still legends speaking of the nabataen's impact even after a more then a thousand years since their genocide at the hands of Nemesis, for instance Petra who speaks about how Byleth's appearance after their fusion with Sothis matches legends from Brigid about people who had spirits inside them. Interestingly enough, you would think that Petra would act uneasy and would talk with less awe about Byleth's appearance if the nabataens as a whole or at least on Brigid were cruel and oppressive tyrants. https://houses.fedatamine.com/en-us/monastery/11#event-base-58-0

Gladly! So language nerd me has a whole thing where Byleth is actually taught the Nabatean language by Seteth and Rhea because he only has fragments from Sothis. Seteth has experience teaching Flayn how to write it (not speak it since Nabatean was her first language most likely) and teach about the culture so this is only slightly new, but Rhea does not (unless she taught Sitri but I'm still on the fence on that one) and she's downright giddy at the idea of teaching Byleth all about Nabatea. He's a pretty fast learner on account of Sothis luckily so it's almost like a refresher course on things he just forgot. Rhea does something she hasn't done in a very long time and takes Byleth to Zanado to explain what the city was like on her own terms in ways that she only can in Nabatean. The trip does help them both through putting Byleth's mind and memories at ease, and letting Rhea have just a bit of closure through just being able to talk about it to, essentially, a lost family member. He also has a much easier time talking to Indech and Macuil since both of them express themselves best in their native language.

Byleth also connects a lot with those two through them helping him with the dragon stuff. Just flying across the desert with Macuil and swimming in the lake with Indech does wonders of getting them to open up . They, along with Rhea too, help him control his transformation along with just his mobility in dragon form. Indech and Byleth particularly get along cause both of them don't speak much so they can just sit together next to the lake in utter silence just enjoy each other's company and they like that.

KINGDOM OF NABATEA: 

THE Nabatean Kingdom was a powerful political entity which flourished in the region of modern-day Jordan between the 4th century BCE and c. 106 CE and is best known today for the ruins of its capital city of Petra. Although it is clear that a wealthy community was thriving in the immediate vicinity of Petra by 312 BCE (attested to by the Greek expedition mounted against it), scholars usually date the Nabatean Kingdom from 168 BCE, the date of their first known king, to 106 CE when it was annexed by the Roman Empire under Trajan (98-117 CE).

Nabateans were Arabian nomads from the Negev Desert who amassed their wealth first as traders on the Incense Routes which wound from Qataban (in modern-day Yemen) through neighboring Saba (a powerful trade hub) and on toward Gaza on the Mediterranean Sea. Their constant travel on these routes intimately familiarized them with the area and their skill in finding, and preserving, sources of water enabled them to transport goods more quickly and efficiently than others.