The Korean war was 70 years ago under extraordinarily different circumstances. Times are different, our available options are different, the geographic locations and relationships are different. Hell, if you haven't noticed, we have a massive in the number people dying as a result of war in the past few decades. Economic and Technological forces have made that possible what wasn't previously, ushering in the least amount of conflict the world has seen. You do get to have it both ways because the world isn't the 1950s and the two situations are completely radically different. If you can't understand that the options available in the 1950s to the US, South Korean and other UN forces facing a massive incursion of North Korean aligned forces are completely different than the options we have to dealing with an apartheid state in the year 2019, the level of banal reductionism you're descending to amounts to the point of parody, because I refuse to believe that one could just be willing to say something along the lines of "oh well nukes ended the war in Japan why don't we just use them every time" and be totally serious.