The combat system has been fully implemented and all technologies are available in the tech tree regarding newer combat units, buildings, and squad sizes. There are several threads on the forums that will give you guidance about the new system. Also there are in game graphics when you hover over a unit to give you a good idea what unit is good against another unit. Research everything you can and look the any guidance you can find on the forums.
That being said, Inno is sticking to their argument that the players have advanced too far. That means that if you have scouted more provinces than the requirements to open the next chest or have not scouted in an even ring around your city, you will quickly run into battles that are extremely difficult and even impossible to win. Inno, through their latest updates, has shown that they are hindering and limiting getting expansions through conquering provinces.