In 1984, why do all three superpowers forbid their citizens from associating with foreigners?

In
Goldstein's book,reads about the goals and functions of the world's three superstates, which
share similar ideologies and are engaged in continuous warfare. Winston reads that the primary
goal of modern warfare is to consume and destroy resources and products, which would otherwise
be used to improve the standard of living in each nation. The authoritarian regimes have no
desire to obtain land or resources from their enemies and simply engage in warfare to cultivate
a hystericalthroughout their society while using up valuable resources without compromising
their industrial capabilities. Essentially, the wars are aused to manipulate, scare, and
economically oppress the population. Winston then reads why citizens in each superstate are
prohibited from being in contact with foreigners.