U.S. policy toward North Korea: The human rights and security linkage
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[T]here is a wider consensus about the undesirability of Iran’s missile activities than there is about how to respond.
There are a lot of vested interests among the Chinese who trade with North Korea. Unless North Korea's actions directly threaten Chinese security or economic interests, it's futile for the U.S., South Korea and Japan to place their hopes on China to deliver a more cooperative North Korea. It's wishful thinking, especially with THAAD which is a loss of leverage for the Americans and South Koreans.
It is also a fact that Beijing cannot control the fast-changing adaptation of Chinese and North Korea business interactions. Since the sanctions, the traders have made the detection of commercial activities more difficult by increasing cash-only transactions and other less traceable forms of funding the commerce.