When the people became a monarchy and demanded a king from Joshua and began to copy the behavior of other powerful and rich countries, the walls appeared in the life of the People of God. But, going back to the Wall of Berlin. I had previously seen many castles, military forts and old cities in Latin America surrounded by walls but all of those walls were only historic monuments. In East Berlin I saw, for first time in my life, the cruel reality of a wall. Walls separate peoples.
Walls divide, segregate and destroy the dignity of the human being.
But we have to be careful when we talk about walls. With technology we can create a wall of energy or electricity or laser. Maybe your eye sees an empty space, but some forces, that any human eye can't see, divides and controls the space. These forces exist and divide and destroy and you don't have to use walls. In the New Testament Paul discovered the kinds of walls that the human eye can't see.