I'm playing through the main campaign as the House of Brutii, and thanks to the earliest Senate Missions I was given I decided to take over Greece. So when they started retreating to Nicomedia and Rhodes, I followed and wiped them out. However, this was right on Pontus's territory, so I set up an alliance with Pontus. As soon as the Greeks were wiped out I planned to break the alliance after sending my own armies near to their main cities, for a swift and unexpected invasion. Needless to say, it didn't go as planned.
I managed to corner the Greeks in Rhodes, so I sent a land army south from Nicomedia to deal with their last army on the mainland, intending for them to meet up with a navy on the south oast of what is now Turkey for the quick hop across to Rhodes. Well,while I was dealing with the Greek land forces the Pontians decided they preferred me as an enemy and decided to attack. I was left facing two forces of Pontians and Greeks with a single force while my navy was all but surrounded by Pontus's own naval forces. It was pretty close, but I managed to get the navy out of there and get to Rhodes and take down the Greeks. Except while I did that Pontus decided to attack all my cities in northern Turkey that I'd taken from the Greeks. I had to fight an entire mini-campaign in Turkey to retake those cities before I could move east. Now I have one city besieged and another two armies converging on my main eastern 'gateway' to Pontus. Time will tell if I can beat them back and continue the eastern expansion... (thank Anoia, rattle your drawers, that my northern borders are all safe thanks to various alliances...).