In Orwell's 1984, Big Brother, the symbolic figure-head for the totalitarian police state regime, holds hypnotic power over the populace, using abusive tactics of the extreme left (communism) and right (fascism).
Big Brother's control lies in his four ministries: Ministry of Love (which tortures), Ministry of Truth (which uses propaganda), Ministry of Plenty (which controls rations), and Ministry of Peace (which wages war). In these four ways does Big Brother and the Inner Party control the masses (the Proles) and the middle-class (the Outer Party).
O'Brien divulges the recipe for control in Goldstein's The Theory of Oligarchic Collectivism:
[Big Brother's] function is to act as a focusing point for love, fear and reverence, emotions which are more easily felt toward an individual than towards an organization.
Big Brother maintains power through pervasive surveillance and total control of information, food, law enforcement, and economics, creating instability and disorganization in the masses. No one in the Outer Party knows who for sure is friend or enemy: this is the genius of the Inner Party. It can both control using a ubiquitous figure-head (Big Brother) without really being blamed for abuse (because no one appears to be in charge).
War is essential to keep the masses poor, hungry, and humble. Counterintelligence and propaganda cause a breakdown in family stability and make relationships nearly impossible.
Finally, fear is used to intimidate and break the will of the people. The symbol of the state's boot heal crushing the skull of a citizen is the dominant image that resonates in the novel--this is what will be remembered of the 20th century. The mass genocide caused by state-waged war against its enemies and its people is the legacy of 1984 and its era.