The relationship between the massive carpet bombing of Cambodia by the United States and the growth of the Khmer Rouge, in terms of recruitment and popular support, has been a matter of interest to historians. Some scholars, including Michael Ignatieff, Adam Jones and Greg Grandin, have cited the United States intervention and bombing campaign (spanning 1965–1973) as a significant factor which lead to increased support for the Khmer Rouge among the Cambodian peasantry. According to Ben Kiernan, the Khmer Rouge "would not have won power without U.S. economic and military destabilization of Cambodia. ... It used the bombing's devastation and massacre of civilians as recruitment propaganda and as an excuse for its brutal, radical policies and its purge of moderate communists and Sihanoukists." Pol Pot biographer David P. Chandler writes that the bombing "had the effect the Americans wanted – it broke the Communist encirclement of Phnom Penh", but it also accelerated the collapse of rural society and increased social polarization. Peter Rodman and Michael Lind claim that the United States intervention saved the Lon Nol regime from collapse in 1970 and 1973. Craig Etcheson acknowledged that U.S. intervention increased recruitment for the Khmer Rouge but disputed that it was a primary cause of the Khmer Rouge victory. William Shawcross writes that the United States bombing and ground incursion plunged Cambodia into the chaos that Sihanouk had worked for years to avoid.