Thanks jonblend for the guide. I realised that I made a BIG mistake in using Esperey as an inf general.
Also thanks to scipioafricanus for his guide for
Establishment of RSFSR. Unfortunately, the princess item "Tourmaline Brooch" does not work. The city info shows -35% constructing buildings cost. The actual reduction is still 25%. I have reported the bug to EasyTech.
My zero medpack strategy which is modified from jonblend's.
The team:
Put Joffre on armored car. (He is the 5th strongest cav general. Also useful in conquest.)
Put Macmahon on old guard. (He is my #2 inf general.)
Put Guepratte on Howitzer.
Put Esperey on Field art. (I wasted 45 books in changing him from inf general to art general, should have convert him to art general in the first place.)
In turn 1, build a university and a palace for Sophie (-35% art cost). Recruit a light art for the first 2 turns (3 if Luise's princess item works, i.e. -35% constructing buildings cost. Use the third light art to help capture the northern city). Use promotion on Joffre. Formulate "air bombing" whenever there are enough knowledge. Kill/cripple as many enemy units as possible. This will enhance the survival of allies which will help to capture the northern city.
In turn 2, use promotion on Joffre again. Use Macmahon and Joffre to attack/block enemy cavs (to protect arts). Use the arts to attack enemy fort next to the middle city (should be destroyed in turn 2 or 3). This will cause less damage to allies which are actively attacking the middle city and also make room for building forts.
Only use the HMGs to attack enemy units that can not counterattack (such as field art or near dead units). Try to avoid as much damage as possible and wait for Macmahon to attack the northern city.
After capturing the middle city, build a military academy and a palace for Luise (-25% or -35% constructing buildings cost). Formulate "air bombing" whenever there are enough knowledge. Demolish the stable (may need to occupy before able to do so if last occupied by enemy).
Build 2 forts when possible. Use them to block enemy units. The tanks will attack the forts rather than the city.
Kill all enemy units near the city, especially von Boehn (tank). Once cleard, leave a militia to guard the city and move all units to attack the SE city. From mid to late game, the allies will help to protect the middle city.
Use spy on the 2 forts near the SE city when troops are nearby.
Build a university after capturing the SE city and recruit a militia to guard it. Continue towards eastern city.
Move Macmahon towards the northern city in turn 3. Attack the northern city together with the HMGs. After capturing the northern city, you'll get 300 gold which will help in building forts. Build a palace for Iriana (-35% infantry cost). Recruit a light inf in the first few turns to defend the city. A problem occurs when the allies capture the city instead. You won't get the gold but have to help defend the city. Allies will spam an inf every turn but the old inf was programmed to rush to attack the eastern city rather than defending the northern city.
Use all the air bombings on Ludendorff (tank). He'll either rush to the northern city or stay at the eastern city. He has an ambulance coach so start bombing him when he's near the northern city or your arts are within range to attack him.
Build the remaining forts when the middle city is not in threat. No need to wait for completion. Just demolish and rebuild. It can be all done in one turn.
The difficult part for this campaign is not in fighting but building 6 forts in 13 turns. The reward "military trucks" (+25% mission rewards) is next to useless. Anyone attempting this campaign would have lots of surplus coins and medals. So attempt the campaign just for fun/challenge.