I believe that is constraining our military options -- the fact that North Korea would target civilians.
There were estimates, at one time, of one million dead civilians in Seoul, South Korea.
Then there is the Winter Olympics scheduled in a few months in South Korea.
Basically, the Olympic site is about the same distance from the DMZ as Seoul in.
Also, I am not much of an expert in these matters.
I did, however, read the official US Naval History of World War II by Samuel Morrison -- which was interesting reading...
Targeting civilians is what dictators do. An overwhelming preemptive strike would be the best solution.