Let’s assume North Korea, in an attempt to show up the United States, launches a nuclear weapon at an unihabitated (or extremely sparsely populated) part of Alaska. What type of options would the United States have? An immediate land invasion by US forces across the 38th parallel? A retaliatory nuclear strike upon North Korea? How would the Chinese, Russians, and Japanese react?
I believe China would advise the US that a nuclear strike on North Korea would be considered an act of war against China. The Russians and the Japanese would also strongly urge the US to reconsider any nuclear attacks.
I’m sure it wouldn’t take long to mobilize US and South Korean troops on the Korean Peninsula. I’m not sure they would be able to invade and occupy North Korea without a serious loss of life. As the US military is streched painfully thin, I wonder if air strikes would be a reasonable option?
Perhaps the North Atlantic Council would invoke article 5 of the NATO charter. Could the combined forces of NATO sucessfully invade and occupy North Korea while keeping Russia and China out? The Germans and the French might have more pull with Russia and China than the US does today.