I was using the US and Iran as an example. The question was more geared toward removing a rogue state. That's why the thread is named as it is. Although, now that i look at it i see i misspelled rogue.
You two are looking at this question from a political position. If I wanted to know the political fallout to a third US invasion i would go ask this question in the political section.
It's pretty hard to avoid politics when you are talking about invading another country. That's an inherently political operation. The neutron bomb that you mentioned was actually designed to only kill living things, by the creation of a large neutron flux, while
not destroying physical infrastructure. Some relatively short time after the blast, we could theoretically come in and get all their weapons, plasma TVs and toasters, with only the rotting carcasses of people, cats, dogs, and wildlife to contend with. Awesome idea, huh?
I think the most effective way to deal with rogue states is to contain them and try to flip them to a non-rogue status. Rogue-ness is mostly a function of leadership. If you can find a way to remove support of the people for their leaders, that would probably be a start. Sanctions are the present method of choice, with a mixed record of success. Libya good, Iraq bad...
A failed state is a different story, and might be easier to deal with. The represent a different threat, since there is no powerful central entity to do things like design and build nuclear weapons and delivery systems.
I know this is about rogue states in general, and not specifically Iran, but since you brought it up, I will note that despite claims by some that they could have "a bomb" in as little as a year (which I consider to be on the verge of, if not exactly fear mongering), that is a far cry from having a
deliverable weapon. It's relatively easy to make a large, heavy uranium bomb. It is much much harder to make a bomb small enough to put on a missile with decent range. I'm sure that a great fear is a smuggled bomb, but we have the technology to spot radioactive signatures at a distance, so countermeasures for such devices exist. I don't believe that the Iranian leadership is insane, despite Ahmedinejad's insane-sounding rhetoric. He doesn't run the country. If they managed to build a bomb and use it against a western nation, they can count on the destruction of their nation, and they are surely aware of that. They have another game in mind. Ahmadinejad is speaking to a more local audience.
ps: I fixed the spelling error in the title.