This new story I'm writing was born out of a dream with an excellent screenplay! :D
Basically what happens is, its a regular workday when the city is suddenly hit by tornados and hurricanes. Things are flying every which way and just as people are scampering for shelter, there's an onslaught of explosives (any other means of attack would work too). People, police, and army (of the victim area) first caught unawares by the natural calamities, are less effective/prompt in responding to the attacks. So damage to life and property is much higher.
- How would the offending army learn about the impending disaster, but not the victim group? Corruption and inside job are a possibility, but how can an entire country/region be oblivious to a destructive force of nature coming their way?
- In the face of a strong and destructive force of nature, which cripples the victim people (think hurricane Katrina or the 2004 Indian ocean earthquake & tsunami), how does the offending group stand strong enough to attack?
Answers to these questions will help me draft the action plan for the victim government, to give them the best chances to fight back now (after the initial shock), and to be prepared for a similar attack in the future.
P.S: There's no magic in this world. Advancement in technology is comparable to present day world, at least in the fields of meteorology and warfare.
Edits: Even an event as major as a meteor could work, IF the attackers could survive that. So basically, the limits of the question extend to whatever they can survive, but the victims cannot. But that's too broad. And I'm thinking they'd like to use forces that are more frequent and probable in a given region, like earthquakes in earthquake prone areas, and hurricanes in, well, hurricane prone areas. So I'm limiting the scope to terrestrial forces of nature that are a pattern for that part(s) of the world.