Gameplay Question

[Matterhorn]

I apologize if there is already a thread on this. (I am playing on H/H difficulty)

Is there a way to, while playing as the Western Roman Empire, prevent the Eastern Roman Empire from breaking it's alliance with me the first turn and then subsequently move 5 full-stacked armies into my Illyrian territories? I guess it's not a complete gameplay, killer, it's just annoying as can be, and the game won't let them attack me (they besiege a town during their turn and during my turn we are neutral again).

I don't have the strength to fight them, and they can't do any damage to me, if I am smart enough to keep my armies in the cities. It is, however, annoying and I was wondering if there was anything I could do to prevent it. If it's a script thing, it would be odd since it was my understanding that after the civil war between Arbogast and Theodocius wars between the East and West stopped for the most part.

Thanks for any help.

[BroskiDerpman]

I was lucky enough that they didn't declare war on me during the first turn. But I will be happy if they develop some type of script to make them allies for at least a long time.