One of the major ways that the party manages to maintain power is the existence or maintenance of a constant state of war. Though it is not economically necessary, given that the three super powers have so called "self-contained economies," the destruction of excess wealth that occurs in the constant warfare allows them to maintain a constantly low state of living for most of the population.
The idea is that if people grew more comfortable and had more time to think and be at rest, they would start to question the authority and this would lead to a loss of control. So to maintain this control, a constant state of war and a poor standard of living must be maintained.
O'Brien points out that the Party has not made the same mistakes as past totalitarian states. The party doesn't seek to rule people through fear. The party seeks to "cure" dissenters of any misunderstandings they may have. It is not enough to fear Big Brother, the individual must love Big Brother. It is only when a population truly loves their leader that they will do anything for the good of the leader. Once the masses live for Big Brother (really the party), there is no need for debate, voting or even fear. Power thus becomes eternal.