Corruption is an interesting phenomenon. This article on the Swedish civil service culture and its journey from corrupt in the 1800s to reliable bureaucracy in the 2000s says (my translation):

"This for me is the most important lesson when it comes to fighting corruption in those countries it afflicts today: You can't just remedy it as an illness in isolation in an otherwise healthy societal body, with some miracle pill. Corruption, beyond individual scandal, stems from deeper deficiencies in the financial and political system."

http://fof.se/tidning/2015/10/artikel/sveriges-vag-ut-ur-korruptionens-grepp (Science and Progress magazine, article in Swedish)

Yet in the curious case of Hong Kong, the only story I hear is about just such a miracle pill: From the corrupt 1950s to the splendid 1990s, all thanks to the ICAC, founded in 1974. Was that really the case, or is there more to the story? What allowed the ICAC to be successful? Political will combined with prosperity? Or was there something more?

In particular, though it was probably a virtuous cycle, which influence was the driver: Did corruption mainly go down because the ICAC happened, or did the ICAC happen because the time was right for killing corruption?

https://en.wikipedia.org/wiki/Independent_Commission_Against_Corruption_(Hong_Kong)