Ukraine

Ukraine has been making their way across the river for a month or so. They took a small foothold a while ago, but the raids have been escalating quite a bit.

That part of Ukraine is some rough territory. Not only do you have the river to cross, there is what amounts to a mini-desert there as well. Roads are a bit farther apart as well. If you saw any videos of troops fighting in what looks like swamp, that is where the majority of those videos come from.

Russia didn't really fortify that area so if Ukraine can manage to setup a healthy logistics path across the river, they can bypass most of the heavy fortifications to east. For the most part, the troops that are there are Russian Homeland defense forces (I can't remember their proper name) and they are not armed or supplied very well at all.