A city only uses its offence if:

• its country is at war with a neighbouring country
• a rebel city is nearby

A city always attacks the closest possible target. If there is offence remaining after that target, it will attack the next closest, and so forth. If the target city makes defence, some or all of the offence may be absorbed, preventing other farther cities from attack.

The farther the target from the city, the less effective the offence.