how would walls affect people who get isolated in a country and those people who get excluded from in entering the country

Walls are extremely limiting, both for people left outside and for people inside of the walled area.

For people who are isolated within a country, the effect can be that of not knowing much about the outside world. An isolated country is also at high risk for dictatorships and autocracies, as people are more easily manipulated and cannot leave the country if they are unhappy. On the other hand, for those who are not allowed to enter the country, the risk can be being unable to enjoy the benefits of that country, being unable to reunite with people in that territory and being unable to discover what the country has to offer. A good example is that of North Korea, and the fact that South Koreans have often been unable to reunite with their families due to strict travel controls (although not precisely a wall).