N Korea can NOT flatten Seoul in a few moments' notice because of the following:
1) Seoul is a HUGE city.
2) N Korea actually doesn't have UNlimited number of artillery tubes capable of reaching Seoul. There are hundreds (maybe a few thousand) tubes but these are heavy ones, meaning they would be lucky to get off a shot every few minutes. And they would have to be concentrated in a relatively small area near DMZ to reach Seoul, not smart move considering SKorea/US's jets.
3) You can BEN SKorea/US jets/artillery are already targeted for some/many of the known N Korean artillery sites.
4) N Korea's most interested in preserving status quo for their leaders and the elites that support the top leaders. Flattening Seoul would certainly mean they would be eliminated.
Yes N Korea can damage Seoul, but will not really 'flatten' it. Well, I hope...
There are some very detailed writeups of PRNK's ability to damage Seoul based on open sources around on the web. The short summary is that 'flatten in a few moments' may be an exaggeration, but they do present a very real and very large threat.
They do have a fair number of dug in artillery installations that could survive several airstrikes. The basic template of these installations are bunkers under mountaintops that artillery can move rapidly in and out of. So instead of shoot and scoot more like shoot and turtle up. They may have limited resources, but the PRNK does appear to know how to deploy them quite effectively. Chemical shelling is a particular concern.
It's not that the PRNK would win an outright war, it's that they could extract a massacre no one else wants.
The op was referring to "flatten" in terms of using a nuclear weapon not conventional artillery. Regardless, I think either way is so improbable it probably isn't even worth speculating about.
Neither is NK. They could wreak some havok with conventional weapons, but their last two nuclear tests were 1 & 2 kt, respectively. That's enough to take out a couple city blocks, with a fireball about 100 ft across. Couple that with the fact they can barely get a missile to go into the sky without blowing up, let alone land where they want it to, and NK's nuclear threat is pretty minimal. They'd cause far more damage with conventional weaponry.
Look into how much artillery they can bring to bear on Seoul (they have the world's largest artillery force, and Seoul is only 35 miles from the border).
Current best estimate is about 10,000 artillery shells per minute, landing in heavily populated parts of Seoul. How long that takes to match and then exceed the death counts from Hiroshima and Nagasaki is an experiment which hopefully will never be carried out.
Interesting logic. The government is willing to go to war to obstruct Iran from obtaining nuclear weapons, yet not when North Korea is actually testing and threatening to "target" the U.S.:
I think you answered your own question. It's a lot easier to prevent a country from developing nuclear weapons that it is to confront one that already has them.
Also, different countries and different geopolitical situations. Iran has a few allies among the superpowers (Russia, China), but they aren't very strong allies. NK has pretty strong backing by the Chinese and the US also has to deal with it's allies in Japan, Australia, South Korea, etc.
It's much easier to play hardball with a country when no one is really opposed to you doing so.
I think there is also the issue that Iran is more likely to fight asymmetrically than North Korea would. I imagine that North Korea has all their nuclear weapons mounted on ballistic missiles. Iran on the other hand probably support an asymmetrical war where nuclear weapons are brought into the country by "stateless" terrorists and then deny involvement.
I would also venture that Iran, being a "non-secular" government where the more fundamentalist members see US influence as a threat to their religion and way of life, is more likely to foster radicalists that would try to enter the US with a suitcase bomb. North Korea has completely isolated itself and its people from US influence. Iran on the other hand has "porous" borders that permit western media and western culture to permeate. The permeation of western culture is seen by some as a threat to be stopped.
Edit: can the downvoter, please explain their down vote?
Right, but that's pretty standard. This is a strategy that has existed since, well, before I was born. Nuclear weapons give you a seat at the grown-ups table. It isn't ideal, but it works. North Korea isn't the fear, nor really is the Iranian government. The fear is Iran will leak a weapon to fanatics that are not part of the Mutually Assured Destruction paradigm. That's problematic. There is some old saying about this, but I only vaguely remember it. It was something like You don't fear a country with 10,000 nuclear missiles you fear the lunatic with the small suitcase bomb.
If Paris/London/Berlin were somehow within 30 miles of Iran's border, nobody would think about going to war with Iran so easily. If any major city of western allies was a few dozen miles from Iraq, nobody would've gone to war with Iraq.
Yes, S Korea's not very lucky in the geography department. Actually the whole Korean peninsula.
The US had a brigade of soldiers stationed in West Berlin whose survival time was ~72 hours in the event of hostilities with the Soviets.
We almost went to war multiple times over things like geese flying over radars. Both the US and Soviets played little games like parking ballistic missiles in Turkey and Cuba to measure the reaction.
Iran has the ability to control the Straight of Hormuz. Iraq had the ability to harass shipping traffic in the Gulf. That waterway is far more important to the US (and Japan, and to a lesser extent, China) than Paris, London and Berlin.
A big difference is that PRNK's provocations are mostly about preserving sovereignty and extracting material aid. PRNK is willing to use asymmetric tactics to their advantage, but so far this has been restricted to amassing weapons that threaten the southern population, and increasingly japan. They may be a batty and inhuman place, but their strategic behavior is largely rational self interest. PRNK wants nukes to hold as a trump threat, to then extract a rent.
Iran on the other hand has a much smaller military than PRNK, but is very active in supporting paramilitary groups (aka terrorists, insurgents) that are aligned with their interests. The fear is, they want a nuke not to hold onto, but to give away.
So aside from any domestic political considerations (read as: Israeli lobby groups), the strategic contexts are different in important ways.
It's mostly because we're in a bit of a bind as far as NK is concerned. As long as China supports/props them up we can't realistically 'attack' NK. Once China drops support for them you can bet that the regime will fall quickly, and/or China will smack them down before we even get the chance.
Iran is not a client state of China, though. Few people in the Chinese leadership want a nuclear war with the US, or with anybody else. They will keep Kim Jong Un on a short leash; we in the US can take our eye off of that particular ball.
