You need railways and supply depots. They are damaged in battles. Need to fix them and wait until they deliver again. Also upgrade you railway lines from your capital to cities and depots near the frontline.I was with Bad Supply Penalty. That was i cant push
And i cant do nothing with Logistics to improve, is that an resistance problem? idk
Edit: Now i discovered that no, IS NOT AN RESISTANCE PROBLEM...So now we have the question: How to do it? Because with no Supply i cant just advance and my attack really begins green but turns red too fast. I do not know how to do in this situation and i tried everything with Logistics but with no advances. HELP!!!!