Some years ago, I worked for a defense contractor writing software for the US Army. We had a consultant who had been a company commander in Viet Nam. Mostly he was gregarious and would joke around, but a couple things he said stuck with me.
The first was his account of calling s strike of white phosphorous munitions on the viet cong. I'll never forget the haunted look on his face while he was explaining how it caused terrible burns because you couldn't just put it out with water, the phosphorus would just keep burning.
The second thing was when we asked him where he thought the US might be involved in future wars (this was during the Iraq war). His top prediction was North Korea. At the time I thought that was pretty unlikely. Why would the US want to hey involved in North Korea?
Thinking back, the software we were working on included a map of Chorwon Valley in North Korea. I realize now that the US military has been thinking about NK for a very long time.
So the scary thing about US saber-rattling is that it is almost certainly backed up by a stack of contingency war plans for invading NK that are just waiting for the president's go-ahead.