But why South Korea knew how to manoeuver through these routes and more so China?
When it comes to South Korea and Taiwan: they both had no natural resources to rely on, and the west feared the expansion of communism, so the west didn't apply their usual policy toward these two small countries and let them develop economically for containment of communism (and to show alternatives to their counterparts: the people of North Korea and China).
When it comes to China,a veteran german politician recently explained it in detail :
1) China was a nuclear-armed UN security council member.
2) In the 1970's and 1980's, the US wanted China to become a counterbalance to communist USSR.
3) The West and Japan desperately wanted to get access to Chinas gigantic consumer market of more than 1billion people, so they were ready to allow things that they would have never allowed for other countries - transfer of technology and know how. And despite China taking protective economic measures, the profit for the industrial nations were so incredibly gigantic (and till today they are) that those nations accepted Chinas conditions.
But the german also said, if the west had known how China would develop, they would never have opened up to China.
Unfortunately, Iran cannot go the same way the east-asians did, the circumstances are totally different. The West (but also Russia and China) will not let Iran develop the same way, because of its massiv resources and also because of its geography - the only country bordering the two by far most important energy reservoirs in the world: Persian gulf and Caspian sea.
Iran has to find its own way.
But one thing is for sure: "Moderate" and "liberal" policies a la Rouhani are toxic for Iran.