The empire comes back soonish, after reorganizing their forces, and Xarooda calls for aid. Our MC and the good Rhodesian general who he faught alongside during the civil war are sent by the queen. That arc is after the upcoming one, which is about settling Wortenia and a few incidents involved in that.
Chronologically I think this battle fits in here, but it's really confusing to actually put it here in story order instead of doing a flashback later, since we're not going to think about them for a while. Unless we're just skipping a bunch of story. Story that sets up a few things that happen during the war.