Slitherine

During T65 of my Epirote campaign I invaded Aetolia with a 41 pt. army and defeated the Macedonian 28 pt. army stationed there.
At the end of the turn, though, I found Macedonia has conquered the region "with the support of the population" and now the region is in Macedonian hands with a 59 pt. army emerged from nowhere ...
How is it possible?

The message is just a flavor message indicating a region has been conquered by someone of the same ethnic as the population. But there is no special mechanism there. Probably you did not notice Macedonia had another army moving into the region, it must be in the message log.

I'll try to have a closer look at the messages but what seems strange is that, though I won the first battle and conquered the region, then I was ousted from it without any confrontation with the new Macedonian army, which in the meantime arrived there.

I just found my army retreating to another region ...