The city has been taken over by a hostile army. Build up your army with heavy military hardware and take back the streets and try not to destroy the city while you are at it.
Build structures, train army, destroy enemy castles. Your soldiers will charge and break through enemy defense lines automatically and use magic to assist your corps assaults.
Enemies are approaching closer and soon they will reach your base. Stop them by strategically placing from defense armies to turret towers in their way.