Capturing territories is the bread and butter of your production life. I'm not going to get into what it takes to capture certain ones. Some else has already done that. however its number of territories i will be talking about. Every city can have the same amount of territories equal to it level. Ok , here is the misunderstood part. If you have 2 cities at level 10 apiece, then you can have 20 territories. This should clear some stuff up about repeated attacks.
If you have any more questions about this matter, find me on chat and ask
Therinfox