What social and political developments occurred as a result of the Cambodian ground invasion ?

Between 1965 and 1973, the expansion of the Vietnam War into Cambodia aggravated and radicalized internal Cambodian political disputes. These disputes became armed contests characterized by shifting alliances, regional struggles for dominance including the US, Soviet Union, China and Vietnam.

a rough low estimate of 250,000 people during this period.

In March 1970, a coup was launched against Prince Sihanouk resulting in a new government with Lon Nol at the helm. The coup government made a drastic change in Cambodian policies, deciding to counter the North Vietnamese, in support of the South Vietnamese and U.S. forces. In May 1970, the US and South Vietnamese launched an offensive into Cambodia, with the aim of cutting off North Vietnamese supply routes.

The final phase of the U.S. bombing campaign, from January to August 1973, aimed to halt the rapid advance of the Khmer Rouge on Phnom Penh, in response, the U.S. military escalated air raids that spring and summer with an unprecedented B-52 bombardment campaign that focused on the heavily populated areas around Phnom Penh, but which affected almost the entire country. The sum effect was that while the take-over of Phnom Penh was delayed, hard-liners within the CPK were strengthened.

Fatalities from U.S. bombing were concentrated during the period in which U.S. President Richard Nixon’s administration carpet-bombed eastern Cambodia from 1969 to 1973, although bombings and incursions into Cambodia by the U.S. began in 1965 under President Lyndon B. Johnson and ended in 1975 under President Gerald Ford. More than 10 percent of the U.S. bombing was indiscriminate.