I'm kinda torn on responding to this; I don't want to give anyone any ideas, but at the same time I'd like to share my opinion as well. Being the
selfish little bugger I am, of course, I'll put my concerns aside and take the chance that I actually have an idea worth stealing
I think the next potential attack(s) would be entirely dependant on the motives of the organization, and I see two potential motives that really stand
out. One is a purely militaristic attack, where the organization is truly trying to set up an invasion or otherwise debilitate the victim nation's
response abilities. The other motive I see is a purely terroristic attack, where the organization is just trying to instill fear in the populous
without any further (immediate) agenda.
In a militaristic scenario, I honestly don't think that attacking a single city--even Washington DC or London--would be the best action, and I would
imagine that the organizations have seen that as well. Even taking out the nation's administration would only disrupt matters for a few days until
there was some semblance of organization. In the mean time, the nation would be on highest alert status, and with a nation that has a reasonably
sized military, all bets would be off at the slightest sign of rebellion or invasion.
Most likely, in the militaristic scenario, the attack would be something akin to 9/11 but on a much wider scale. A concerted series of weakening
attacks across the nation, affecting various aspects of infrastructure such as highways, power plants, water supplies, etc., would cripple the nation.
Federal response would be spread extremely thin, and at least in the US most local authority would probably be undermined as the federal government
tries to instill a sense of control. The attacks would probably also focus somewhat on major downtown and metropolitan centers in an attempt to
create mass confusion among the populous, thereby postponing any vigilante reaction until it's too late.
In a strictly terroristic attack, the idea of a widely concerted effort is greatly reduced. It would most likely come in the form of several, almost
unrelated events similar to the 7/7 bombings, or the '93 WTC bombing, and spread out over the course of months or years. Most likely the
organization would wait until everyone is secure, not only to increase their chances of success but also to have the most dramatic affect. They may
take advantage of a natural disaster as well, when everyone is focused on helping out the victims--think about it, how bad would it have been if a
truck load of explosives went through the doors of the Superdome or a small plane crashed through the roof of the NO Convention Center in the days
after Katrina?
One thing that wouldn't surprise me is if the next terroristic attack hits a small town instead of a large city. If I remember correctly, large
cities account for a relatively small percentage of the American population for example, and yet these have been the targets of the majority of
attacks around the world. A bomb going off in New York is more news-worthy than if it were to go off in Podunk Iowa, but it also distances the
majority of the population from the event. Many people end up with a sense of security, thinking "I live in a small town, nothing's going to happen
here." A terrorist attack in AnyTown USA would throw that idea out the window, and many more people would feel the effects of it.