There is also regionalism in play, though it is not as strong as it used to be, especially amongst younger generations.

In particular, the southeast region (Gyungsangdo - GSD) is the core of the right-wing, and the southwest region (Jeollado - JLD) is the core of the left-wing. I really cringe at using the words "right" and "left" here because South Korean politics doesn't neatly align with what many Westerners would think of when hearing those terms. But for lack of better terminology...

In any case, the earlier presidents (or quasi-dictators) hailed from GSD and overtly favoritized their home provinces in terms of economic development, etc. while leaving JLD less developed. This has led to resentments that reflect in politics that persist to this day.

Some would argue the rivalry goes back even further. Historical texts exist that describe animosity between the GSD and JLD regions back into the Joseon dynasty. Going back even further, the GSD and JLD regions were the rival and enemy kingdoms of Shilla and Baekje respectively, the former which eventually conquered the latter.

It used to be that it was even taboo to marry across GSD-JLD lines, but again, this mainly affects the older generations. Personally - while I am Korean-American, my family comes from GSD. My wife is from JLD. My dad is on the conservative spectrum in terms of Korean politics and I was initially worried what he would think when I introduced my then-girlfriend to my parents for the first time. Thankfully it was a total nothingburger and my now-wife and my parents get along absolutely fine.

I once saw a TV clip where they challenged viewers to tell the difference between per-province election results and the response to Sejong's tax system at the beginnings of the Joseon dynasty -- they both had the same GSD/JLD split.

Unfortunately I can't find it now though; it was very insightful.

It's still common in popular media, there was a 2021 KDrama series ( Beyond Evil ) where they reveal who are all the bad guys early with one tell, they were the only ones who ate Japanese food. A 2018 series Mr Sunshine about the lead up to the Japanese occupation generated a bit of controversy because one character that adopted Japanese customs was portrayed sympathetically and they changed the story as the episodes aired to respond.

I am actually surprised there is a small (tiny?) but still surprising number of people that feel Japan is a real, direct, short-to-medium term military threat to Korea, as in the shooting war kind. This is a sentiment I see a lot in the Korea subreddit, but that might just be overly "nationalistic" "Koreaboos" - who may even be mostly Korean-Americans that have rarely set foot in Korea, or not even ethnically Korean.

The sentiment is not non-existent in Korea itself too though. In fact, in some discussions of recent military developments by the RoK (plans for a aircraft carrier, SLBMs, F-35 and/or KF-X fighters, etc.) it's often touted by these folks that they are just as meant to be pointed towards Japan as they are to North Korea or China.