From the Economist:
Ieng Sary

Most of the time I link to articles because I approve of them, but every once and a while I link to an article that gets on my nerves.  This is one of the latter ones.
 When the Khmer Rouge government itself was toppled by a Vietnamese invasion in 1979, he fled to Thailand; and there found fresh clothes, new sandals and a VIP air ticket to Beijing, all supplied by the Chinese embassy in Bangkok. His skilful contacts with China kept the movement going for two more decades.

If you read the article, the Chinese get all the blame for diplomatically and economically supporting the Khmer Rouge after the 1979 Vietnamese invasion.

It is COMPLETELY absent from this article that the United States also condemned Vietnam's 1979 invasion which removed the Khmer Rouge from power.  The US (and its allies) supported the Khmer Rouge against the Vietnamese backed Cambodian government throughout the 1980s.  During the 1980s, the US and its allies refused to allowed the Cambodian government in Phnom Penh a seat at the United Nations, and instead the US allowed Khmer Rouge (in exile in Thailand) to retain the UN representation. 
Furthermore, in the Economist article it is only briefly mentioned that the Khmer Rouge were allowed to operate out of bases in Thailand during the 1980s, and never mentioned that Thailand was a U.S. client state in the cold war era.
 Instead, it's all China's fault.

In fact most Americans don't even know the United States government supported the Khmer Rouge against the Vietnamese in the 1980s.   And the way history is routinely whitewashed in the American media, with articles like this, is it any wonder?

  See wikipedia article here (Khmer Rouge: The Place in the UN) and here (Khmer Rouge: The Ramifications of Vietnamese Victory).  Also see On the Side of Pol Pot: U.S. Supports Khmer Rouge