**Nuke it from orbit.**

It's the only way to be sure.

This might be a pretty boring answer, but if your obstacle is a city, and removing the city would give you success, then that problem is fairly easily solved. Bombing cities has been the best way to destroy cities for a long time now- why change the status quo?

Yes, yes I see 

> PS: No nuclear weapons. I have a severe allergy to nuclear detonations.

So **conventionally bomb it from orbit**. (A much less catchy and memetic headline though...)

We have [pretty big non-nuclear bombs][1]. And who says you have to just use one anyway?

Or not from orbit... drone bombers would probably be more effective anyway...

If you actually want the "orbit" part, or have something cooler than normal bombing- [just drop stuff on them from space][2]. It's called kinetic bombardement and I hear it's pretty deadly...


  [1]: http://www.popsci.com/military-aviation-amp-space/article/2009-08/pentagon-wants-deploy-largest-non-nuclear-bomb-next-year
  [2]: https://en.wikipedia.org/wiki/Kinetic_bombardment