Following the March 1970 coup led by the pro-U.S. General Lon Nol, the PAVN aggressively expanded their control over the provinces of northeastern Cambodia, coming dangerously close to the capital Phnom Penh.

By April 1971, Lon Nol decided to renew the offensive against the PAVN/VC forces, taking advantage of the high morale among the FANK troops following the partial success of Operation Chenla I.

Phnom Santuk was eventually retaken, and the first phase of Chenla II was declared officially concluded on 25 October, although real military success had not yet been secured.

Victory celebrations had hardly started at Phnom Penh when on the night of 26 October, barely hours upon the conclusion of the consolidation efforts of the second phase of the operation, the PAVN 9th Division, reinforced by the VC 205th and 207th Regional Regiments, launched an all-out assault on the Cambodian positions located along Route 6 from the Chamkar Andong rubber plantation.

Elements of the PAVN 9th Division then launched a final attack which ripped apart several FANK and Khmer Krom battalions, causing the disorganized Cambodian troops to abandon several key positions on 1 December.

From then on, the Republican government focused on consolidating its hold over the key urban centers, the main garrisons and the lower Mekong-Bassac river corridors, thus leaving most of the countryside virtually open to Khmer Rouge recruiting drives.