NK doesn’t pose a credible military threat to the US. It poses a credible military threat to SK. That’s why the US acts as a deterrent.
Of course, if Rome's interests are not threatened, then it's those of Rome's allies. Nevermind that SK outspends NK on the military, or that the north hasn't attacked in 70 years.
The difference being: the US can afford to spend that money on the military much easier than NK can.
First off, so what? This is a talking point I always see that makes absolutely zero sense whatsoever, to look at expenditure as a percent of GDP instead of in absolute terms. As if it's just natural to keep pouring money into the military for no reason, just because you can!
Military expenditure is only justified if it is countering a real, legitimate threat. If a small poor country is threatened by a large rich country, then the small country is of course justified in spending a higher percentage of its GDP on defense, because otherwise it would be completely defenseless. Conversely, to spend not only more than any other country, but more than the next nine countries combined, clearly means that the expenditure has nothing to do with responding to threats. Rather, it is about being a threat, which other countries then have to respond to.
Secondly, I disagree that that the US can more easily spend the money. Because, despite how much richer the US is, it is also trying to hold together a globe-spanning empire through military force. Korea is only one of many theaters that the US is involved in, and what we're seeing now is that the US is being forced to pull military equipment away from Korea to the Middle East, where it's once again gotten over it's head. The money that we spend on trying to dominate Korea also has to be spent on every other imperial project, from Cuba to Iran to Syria and so on.
Because of how massively overextended the US is, it is now $40 trillion in debt, many countries are turning to or at least considering dedollarization, and the US is scrambling to make trade deals more extractive which is causing long-term harm to its alliances. And that's just internationally! Domestically, the situation is even worse. Trump rose to prominence in a large part because he distinguished himself from the political establishment, both sides of which fully supported the disasterous, failed imperial project in Afghanistan. The far-right has jumped on the opportunity to take advantage of people'e frustrations with all these foreign entanglements, and the declining economic conditions such as inflation, while holding and promoting all kinds of extremist ideas (and while continuing to engage in such projects). The only prominent voices in American politics with a platform to present an alternative are useless liberals who refuse to adapt to the situation in any way, stubborning clinging the same kind of imperialist talking points you've said and not addressing people's actual material needs.
The longer this situation is allowed to continue, the more likely it is that the fascists will seize power, permanently. If you think things are bad with Trump now, you have no idea how much worse the right is capable of becoming, and how much worse they will become. The US, at present, cannot afford to be involved in any conflict abroad. Frankly, I'm not even sure that the US could fix itself if it did drop everything and adopt the correct focus. The core of the empire is in a state of decay and crisis. And while that it happening, it absolutely cannot afford to be preoccupied with anywhere like North Korea, which certainly does not present any kind of existential threat.
Every dollar wasted on pointless military exercises on the Korean peninsula is a dollar that isn't being spent revitalizing the domestic economy, and if the economy is not revitalized then it is inevitable that the fascists win. Why should I care about this absurd, exaggerated threat on the other side of the world, when there's an actual, real threat that my next-door neighbors could vote for me to be sent to a camp? It's delusional, it's complete and utter nonsense.
Who cares if the empire is maintained and expanded, if it turns full-on fascist?