Vietnam was the 2nd "hot" battle of the cold war. Korea was the 1st "hot" battle of the cold war. The communists could be contained in Korea, because that country is a peninsula. The US Navy controlled the ocean surrounding that country, therefore the communists could only resupply with men & material directly across the Red Chinese border; easily controlled by US/Allied forces with "Firepower." The US/Allied forces were able to hold the "line" at the 38th Parallel, which still exists today. Vietnam was NOT a peninsula. Communist men & material continued to flow into South Vietnam, via many routes, but primarily the vaunted "Ho Chi Minh Trail"; which despite being bombed into a lunar landscape, could not be controlled. The only way to eliminate or control the infiltration point(s) was to directly (officially) involve the neutral countries of Laos and/or Cambodia. This would escalate the war, adding one to two more countries to the conflict. Secondly, and most important, the communist superpowers; Red China & the Soviet Union could possibly become directly involved in the war. This was a real possibility; Red China had ENTERED the Korean War (1950-1953) when US/Allied forces "invaded" North Korea. The US was determined not to allow that to happen again. Thus, with no way of stopping the flow of communist men/supplies. We "attritted them" in place. "Body Count" became a way of life for the GI's trying to eliminate communists forces. We couldn't eliminate them all, they just kept coming down that trail...the price in GI blood was becoming too high to pay; so it had to end.