Battle of Carpathian guide?

The trick is to take out the middle city before the gas takes you out. If you have strong generals and high leveled up troops, you can take it in a couple of turns before you run out of gas masks. Otherwise upgrade your city to level IV, and upgrade the military tactics to level II to start making gas masks until you take the middle city. Put your best Calvary General on the Cossack, and try to line up every attack with two enemies in a line to get the double hit from the Cossack. Use your artillery general to take out the middle city to take it as quickly as you can, even if you must avoid the fort. Once you take out the middle city and fort, all enemy should come at you, so spawn infantry to hold it and move all of your generals southwest to pick up the lighter guarded level IV city. Once you have those three cities you should have the economy to make enough units to take out the northwest city and general.