How does the Party/Big Brother use war as a method of control in George Orwell's 1984?

The
purpose of war in a totalitarian society is to keep the population under control by having an
outside enemy that it can direct its anger and hatred toward. The conditions of life in Oceania
(and presumably in the other two superstates, Eurasia and Eastasia) are such that people would
inevitably be dissatisfied and resentful. They have no freedom of expression or activity, and
there is no material wealth or any possibility of achieving it. Except for the elite Inner
Party, the people live in a state of deprivation: food is scanty and poor, living quarters are
cramped and dirty, and everyone is under constant surveillance through telescreens. The Party,
by fighting a perpetual war against a mostly unseen enemy, keeps its own people focused on
something external to hate, as an object of their natural aggression, and thereby achieves a
kind of mind control over the population.

The war also keeps people in a
state of fear, and it's through fear that they are most easily manipulated....