The reason that Arista...?

[Sofiab]

I was a bit disappointed that Arista just left her responsibility as a major at Ratibor. I guess i wanted the whole nationalist movement to keep going.

What I wonder is are we supposed to believe that it was some kind of magic power that influenced her to leave? Like either Esrahaddon put some kind of spell on her or the robe made her want to leave.

I haven't read the last book in the series yet so if it's answered there don't tell me what it is.

[Christomir]

No, there wasn't any magic in that. It was just that the shocking way (view spoiler)[Esrahaddon died (hide spoiler)], and the things he told her right there and then, made her suddenly realize that finding the heir and rescuing him would be the overwhelming priority - much more important than the well-being of just one city. But I'm guessing you have already read the entire series, so my answer comes a bit late? :)

[Misha]

Christomir wrote: "No, there wasn't any magic in that. It was just that the shocking way [spoilers removed], and the things he told her right there and then, made her suddenly realize that finding the heir and rescui..."

+1, and also that Arista is the only one who has some fragment of the bigger picture Esrahaddon was working to prevent, i.e. the end of humans. If Arista continued with her administration duties, literally nobody else has the information from Esra to be able to do anything about the bigger issue and so she leaves.