In 1984, why is it essential that the different populations of the three super-states never come into contact with each other?
In 1984 the world is ruled by three giant superstates: Oceania (where Winston lives), Eurasia, and Eastasia. They are in near-constant conflict with each other, driven on by relentless propaganda that paints the enemy as somehow less than human. In Oceania in particular, the populace is encouraged to hate foreigners, and any average citizen who establishes contact with foreigners is committing nothing less than high treason.
So long as this mutual hatred can be maintained, the political elites will be able to remain in control. However, if the people of the three superstates should ever establish contact with one another, then the consequences for the powers-that-be are potentially catastrophic.
For then, the citizens of these states would realize that their counterparts are human beings just like themselves. At that point, they'd also realize that they'd been lied to all these years by their respective governments. This would undermine the ability of each state to control its citizens, as power in the three superstates is largely based on keeping the population in a state of ignorance and fear.
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