How we change what others think, feel, believe and do
Prevent them from traveling, effectively containing them in one place.
Lay siege to their main cities and fortresses.
Blow up bridges and mine roads so they cannot easily travel along particular routes.
Blockade or bomb ports so they cannot receive supplies or support by sea, or otherwise gain naval advantage.
Break up their great armies into smaller units, then do not permit them to reform. Then destroy or capture each unit separately.
If you cannot do this to the entire enemy, do so to parts of it.
Isolation can also be bone politically. Turn all parties against your enemy. Seduce their allies. Conquer their friends. Give them no place to turn for succour or support.
When you are cut off from the world, communication is often difficult, making choosing one's next move difficult. Isolated armies are unable to rejoin a main force and are easier to defeat. This can be a demoralizing position.
Isolation is similar to encirclement but does not force the choice between fighting or capitulation. An isolated force can stay where they are or perhaps move further away in unguarded but unhelpful directions.
In the first Gulf War, the United Nations resolution effectively isolated Iraq and removed most sources of support. In the second Gulf War, initiated by George W. Bush, the lack of UN support means that the US and UK were isolated with very little other support.
In argument show that they stand alone in their position with no supporters and many opponents. Show them there is no-one they can turn to. Show how their views are not shared by others and how they are in danger of complete social isolation.