 Following the overthrow of the Cambodian head of state, Prince Norodom Sihanouk, in a coup d'état in March 1970 and its replacement by the pro-US Khmer Republic, the re-christened Khmer National Armed Forces (FANK) focused on expelling all People's Army of Vietnam (PAVN) and Viet Cong (VC) forces from their border sanctuaries in eastern Cambodia after the new President of the Khmer Republic, Marshal Lon Nol, issued an ultimatum.However, from May 1970, the ill-prepared FANK was quickly placed at a strategic disadvantage following the seizure of the northeastern areas of the country (the provinces of Stung Treng, Ratanakiri, Kratie, and Mondulkiri) by the PAVN in response to the ultimatum and the loss to the Khmer Rouge insurgents of several peripheral eastern and southwestern Cambodian provinces (Kampot, Koh Kong, Kampong Cham, Preah Vihear, plus portions of Siem Reap, Oddar Meanchey, Kampong Thom, Prey Veng, and Svay Rieng Provinces) during that same year.In July 1970, the FANK High Command decided to take advantage of a lull in PAVN/VC activity as an opportunity to regain the strategic initiave and raise the morale of the FANK troops by retaking large expanses of rich rice-growing areas in northeastern Cambodia not under the Khmer Rouge control.