Yet, for years after the Khmer Rouge regime fell, the United States continued to officially recognize its leaders, who had fled and resumed guerrilla warfare, as Cambodia's legitimate representatives in the U.N. That fact still rankles Hun Sen, who often raises it when feeling aggrieved by U.S. policy.
A sign on the Peace Palace's exterior wall on Monday welcomed the arrival of Chinese Premier Wen Jiabao for the summit. There was no similar sign heralding Obama's arrival.
Hun Sen's reputation for violence owes much to the fact that he staged a 1997 coup against his own coalition government. Forces loyal to him defeated those of his co-prime minister — whose party had actually won elections four years previously — putting Hun Sen once again in full control.
By hook or crook, he has remained in power ever since, winning several elections.
In recent years, Hun Sen's opponents have been more likely to stand before a judge than stare down the barrel of a gun, human rights groups say.
Last month, a court sentenced 71-year-old Mam Sonando, owner of a radio station that is one of the country's few free media voices, to 20 years in prison on insurrection charges that critics say were trumped up to silence him.
Opposition leader Sam Rainsy — the sole Cambodian politician with the charisma and resources to present any real challenge to Hun Sen — is in self-imposed exile to avoid 12 years in prison from convictions critics say represented similar political persecution.
Unless Hun Sen sees an advantage to having him pardoned, Sam Rainsy will likely be shut out of next year's general election and his party will lose its best campaigner.
Economic development is a particular point of pride for Hun Sen's government, bearing in mind the low point growth started from — the Khmer Rouge had even abolished the use of money.