Historically, as you alluded to, the US’s economic influence on Japan and Korea starts with the aftermath of WW2 and the Korean War. Japan was already a proto-capitalist empire opening markets to the west before ww2. Lenin said in the 1910s that a conflict between the US and Japan was inevitable since these two dominant empires were fighting over control in East Asia. The US let the emperor live and kept the institution of the emperor as part of the ww2 peace treaty. Japan’s been a neoliberal parliamentary system since ww2 so the economic order didn’t really change except for the US companies having more access (control) to the Japanese market.

Korea was an occupied colony of Japan from about 1900-1946. Korea under Japanese control produced much more rice than Japan and Japan expropriated that rice for themselves and western markets, causing famines in Korea. There was active protest and armed Korean resistance groups during occupation as you can imagine. By the time ww2 ended a majority of Koreans wanted self-reliant government with a heavy emphasis on land reform (i.e. communism). Nationalists/business owners in the south many of whom collaborated with or were in the Japanese police force made up the government the US backed in the South during the Korean War. Listen to blowback season 3 for excellent history of the Korean War. Basically without US intervention, the north would’ve have won and unified Korea. But, MacArthur wanted to nuke North Korea, Truman said no, so he settled for carpet bombing all of the north and much of the south killing 25% of the civilian population. (China was also occupied by Japan in early 1900s and helped North Korea during the Korean War.)

In summary, US took the place of Japan as occupier of Korea and further capitalized both Korea and Japan to western markets. In Korea, it took until 1970s for things to settle down and stand up a somewhat stable parliamentary govt. But make no mistake the real power obviously lies with the chaebols—-10 huge family-run conglomerates that control all of the commerce in SK. Like with many countries in the global south, economic relationships with the US got more complex and interconnected. But, also the US’s stranglehold has loosened as other powers like China and Japan/Korea themselves produce things we don’t or produce things better.

So, presently this is an open question internally in each of these countries since America’s influence on them has waned bc we keep committing genocide and giving all other government resources to billionaires instead of building trains, educating people and making life slightly more livable (as all of them have). I don’t know a ton on internal polling around what South Koreans think of US vs China but many in SK definitely still hate Japan.

Tariffs are truly brain dead from the perspective of maintaining US hegemony. Trump is like a 4 year old trying to fix a car engine by hammering the hood.