text: Operations During Armed Conflict
  Defeat of the North Korean People’s Army, September 1950
  In early August 1950, the North Korean People’s Army (NKPA) advance had driven
  U.S. and Republic of Korea forces back into the southeastern portion of the Korean
  peninsula and threatened to push them into the sea. To stop the advance of the NKPA,
  U.S. and Republic of Korea forces held a defensive perimeter, approximately 140 miles
  wide, along the Naktong and Nam Rivers. Over the next few weeks, NKPA and friendly
  forces engaged in heavy fighting with attacks and counterattacks occurring along the
  entire perimeter, as the NKPA attempted to break through the defensive line.
  Throughout this period of the war, the NKPA held the initiative against U.S. and
  Republic of Korea forces, but by mid-September the initiative shifted to friendly forces.
  On 15 September, while United Nations and NKPA forces were decisively engaged in
  the south, the U.S. X Corps conducted a two-division amphibious landing at Inchon,
  on the west coast of Korea, north of Seoul. This operational-level turning movement,
  code-named OPERATION CHROMITE, occurred 150 miles behind enemy lines and
  caught the NKPA completely by surprise. In the following days, X Corps captured the
  Seoul-Suwon area and severed NKPA lines of communications.
  In conjunction with the amphibious landing, the U.S. Eighth Army launched a major
  counteroffensive against the twelve NKPA divisions opposing it in the south. With the
  support of United Nations’ air power, the Eighth Army penetrated the enemy’s forward
  defenses at multiple places and advanced northwest to link up with the X Corps. The
  combined actions by X Corps and Eighth Army left an estimated force of eight NKPA
  divisions isolated in southwestern Korea. Outflanked, unable to resupply or reinforce,
  and facing strong pressure in its close and rear areas, the NKPA began to collapse.
  Some NKPA units and individuals began to retreat, and their initial retreat quickly
  turned into a rout. Those NKPA units unable to retreat were destroyed or captured by
  friendly forces. By the end of September, the NKPA ceased to exist as an organized
  fighting force in South Korea.
  ISOLATE
  6-117. Isolating an enemy force separates it from its physical, information, or human sources of support. It
  involves denying the enemy force access to resupply of personnel and equipment, access to intelligence, and
  shared understanding with adjacent units and higher echelon headquarters. Isolation denies enemy ground
  forces access to capabilities from other domains, forcing them to operate only in a limited area of the land
  domain with the resources they have on hand.
  6-118. At the operational level, it is difficult to achieve complete isolation of an enemy force not already
  physically separated from the enemy main body. Even limited access to air, ground, and maritime lines of
  communications can sustain a prepared and determined enemy force for long periods. However,
  operational-level commands can employ capabilities to temporarily isolate units or critical capabilities from
  the rest of an enemy formation in one or more domains. This enables defeat of the enemy in detail, or it sets
  conditions for operations in other domains. Operational headquarters conduct activities that physically and
  psychologically isolate enemy leaders from their formations and other sources of support. This may include
  disrupting communications networks or access to space and cyberspace capabilities for a specific enemy
  echelon or conducting influence activities to lessen local support for national objectives. When an enemy
  force includes elements from different nations, it is possible to isolate one or more of them physically or by
  informational means. Exploiting differences in national aims or cultural divisions degrades the enemy’s
  overall effectiveness.
  6-119. At the tactical level, physically blocking lines of communications, controlling key terrain, fixing
  supporting units, and encircling an enemy force are tactics that support the achievement of isolation.