The second city in the game can be unlocked by obtaining 30 city key shards in the game.
Obtaining a Second City Edit
In order to obtain a second city, the player must obtain 30 city key shards through purchases or through daily VIP reward (when over Command Center 12). A full key can also be bought through the 'Second City' bundle.
Once the key is obtained, the player must then choose a location to place their second city. Many players often choose to build right next to their first city, as it enables them to easily send resources and reinforcements back and forth.
Hero II Edit
When you build your second city, you will be faced with a city similar to your first city when first starting out, with some minor rearrangements of buildings and building plots. Not only this, you will be tasked with leveling up a second hero. It is advisable to continue supplying your first hero with the bulk of the xp, such as that obtained from missions and chests.