Main City, and Sub.

The main city and Sub-city
1, Why Sub-city?The first Sub-city is usually used to offering more resourse, and the 2nd and 3rd for setting your soldiers. 6T means the city has six Farmland and 15T short for 15 Farmland.

2, How can build first Sub-city?
With Mansion or Annexe in first city reached level 10 and Commercial Value of your city (seen from Mansion or Annexe) reached 1200. but before you do that you should call 3 Pioneers in Mansion or Annexe,then click on the map where you wanna build your new city.(Mansion can not exist with Annexe in one city.)

3, How to build more sub-cities?
Mansion in main city reach level 15 and 20, you can call second and third 3 Pioneers in Mansion(Annexe is level 10 and level 20,2 times).But usually we will upgrade Annexe in the first sub-city to level 10, and call 3 Pioneers to build 2nd sub-city. In 2nd sub-city, do the same to build 3rd sub-city. That will save your time and resourse and have chance to build more sub-cities!

4, Difference between main and Sub-city.If you have cities and build Mansion in one of them, then the city will be main.The Farmland in main can reach level 20 while Sub-city 10. If change Sub-city into main, the Farmland and other resourse higher than level 10 in old main city will down to 10. Be careful to change your main city.

The Commercial Value to build a sub-city: (Number of Sub's first, then commericial value needed).
01 1200
02 8000
03 20000
04 39000
05 96500
06 160250
07 237600
08 329400
09 432675
10 615425
11 821125
12 1086325
13 1379150
14 1700450
15 2051075
16 2431875
17 2843700
18 3287400
19 3763825
20 4273825
21 4818250
22 5397950
23 6013775
24 6666575
25 7357200