Yeah, the Japanese didn't start the all out push to "Japanize" Koreans (and Taiwanese) until World War II. Until then they largely paid lip service to eventual independence while refusing to ever really see either group as having the potential to be considered full subjects equal to themselves or actually considering giving them freedom.
I guess this is true, but WWII was brutal enough.
Exactly how much harsher was Japanese rule in Korea as compared to Taiwan? In the latter it was a fairly standard colonial experience of unfair policies designed to help the colonizer at the expense of the colonized mixed with rapid economic growth and development. The idea that Japanese rule in Korea was comparable to German rule over Poland seems extreme to me. Their actions in China certainly fit the bill, but Korea? To me the intensity of Korean hatred for the Japanese seems to come more from the humiliation of being colonized by a culturally similar neighbor which had for centuries been seen as inferior than the reality of Japanese rule on the peninsula. Not to say it was rosy, as colonial rule never is, but it was hardly an out and out concentration camp/mass slavery/intentional genocide type situation.
The comparison of Koreans under Japan to Poles under Nazis is actually fairly apt. There is, however, a major difference, which lies in the significant difference between the Nazis and anybody. That is to say, Nazi policy, in the long term (and as something which applied to all "Non-Aryan" races), was the total extermination of Poles, Poland, and Polish culture. Nazis are unique in this respect, as this is a level that even Japan did not stoop to (though they did intend to figurative extinguish Korea as an independent state and Korean culture), even if it was only for practical reasons.
IMHO, I think it's almost impossible to compare the Nazis to the Japanese in the first half of the 20th century on an equal basis, because the former were in power for a shorter amount of time. However, I feel that both were brutal in their own ways. Here's part of what I posted earlier:
Along with comfort women. Also, after the March 1st Movement in 1919, the Japanese tortured and/or executed thousands without trial. They also distorted Korean history in order to justify their rule by systematically compiling records and producing their own version, while relocating a large amount of artifacts to Japan. The Japanese also banned the Korean alphabet after 1938, and omitted any mention of Korean history in the school curriculum. Most of the structures around Gyeongbokgung, the main palace, were destroyed, and the General Government Building replaced the palace.
Koreans were required to maintain Korean names from 1911-1939 in order to distinguish them from the Japanese. Also, until 1939, a significant amount of the population did not have a surname. The name change policy (Soshi-kaimei/Changssi-gaemyeong) was implemented in 1939, and it was strictly enforced to the point where rations were not handed out, students were expelled, and people were fired from their jobs if they did not adopt Japanese names.
The Nazis came to power in 1933, and started expanding (with the exception of Austria and Czechoslovakia, which had large Austrian and German populations) into other countries in 1939, when war broke out. It collapsed in 1945, which means that most of its policies were carried out during wartime. On the other hand, the Japanese began to colonize Taiwan in 1895, Korea in 1910, and maintained Manchuria as a puppet state starting in 1932. In other words, while a significant amount of its policies were carried out during World War II, they were also heavily influenced by the ones that came before the war.
In terms of Japanese rule over Korea, the former was mostly concerned with suppressing anything related to independence until 1919. After thousands were imprisoned and tortured in the aftermath of the uprising, the Japanese decided to loosen some restrictions in order to prevent similar events from happening again in the future. However, they continued to suppress Korean culture by compiling a fabricated version of Korean history in 1925, which would have been a tedious process. Attempted coups then occurred in Japan in 1932 and 1936, which caused the military to become more unstable, and education banned Korean history, while restricting and eventually banning the Korean language by treating as nothing more than a dialect during this time. Meanwhile, Shintoism became the state religion, and throughout the 1930s, the Japanese began promoting an ideology in which Japan had supposedly ruled over Korean states as tributaries.
In other words, the name change policy, which was probably the only time in which an entire nation's population was forced to legally change their names systematically, was only the culmination of a process to gradually assimilate Koreans, in which they would be wiped out as a separate ethnicity. The difference between Poland and Korea was that Germany planned on replacing the country with settlers, while Japan decided to assimilate the population. However, Germany attempted to carry out its policies by invading and administering the territory, while Japan already failed to do so during the Seven-Year War (1592-8), and decided to annex the country, then focus on destroying the culture and identity of the country altogether.