There is a pattern through history of empires building walls when they reached maximum expansion. Consider the Great Wall of China, the wall the Romans built to keep out the Goths, the Berlin Wall to preserve an island of Communisim in Germany. Walls save a lot of time and energy, as you don't have to have as many soldiers patrolling the line. Walls are built when the empire admits they can go no farther. We build walls because we are afraid. Often because of what we fear is on the other side, sometimes to protect what is inside. For instance, we build baby gates and playpens to protect our young ones from the ordinary dangers in our own homes.
Besides the Berlin Wall, communists used other means to keep venturesome ones from travelling too far. For instance they would require loved ones remain behind when diplomats or athletes necessarily interacted with the outside world. What did the communists fear in this case? That the outside world would not be as fearsome as it had been portrayed back home?
What is the Watchtower Society so afraid of?