From what I've read, it's never stated specifically one way or the other. The information Konami has released on the events of the Higheast Rebellion is pretty vague. The only specifics that I know of for sure is that in 472 Harmonia worked with Highland loyalists in Dunan in an attempt to retake the Higheast Province, and that Harmonia tried to legitimize this action by making the case that they were entitled to this land since it used to be their territory and they were going to try to restore the Highland royal family to power. It was resolved when Shu came out of retirement to cook up a plan that would stir up internal trouble in Harmonia, which eventually led to the Harmonians withdrawing their troops.
As far as I know that's the only "official" information, but the whole thing is fun to speculate about. I'm currently working on a fanfiction project based on the Higheast Rebellion, and it has been a lot of fun to work with the basic outline and expand it. But still, those are just my speculations. And unless Konami decides to release more details about the Higheast Rebellion, that will be the only thing we know for sure.