Demonizing the enemy, demonization of the enemy or dehumanization of the enemy is a propaganda technique which promotes an idea about the enemy being a threatening, evil aggressor with only destructive objectives. Demonization is the oldest propaganda technique aimed to inspire hatred toward the enemy necessary to hurt them more easily, to preserve and mobilize allies and demoralize the enemy.
Because of the frequent misuse of the term demonization, it is deprived of its potential to be analyzed. That is why Jules Boykoff defined four criteria of enemy demonization:
The demonization of the enemy has been routinely conducted throughout the history. Thucydides recorded examples in Ancient Greece.
Phillip Knightley believed that demonization of the enemy (first enemy leaders and later enemy individuals) became a predictable pattern followed by Western media, the final stage being atrocities.
During the Second World War, propaganda documentaries that contained enemy demonization and flag-waving patriotism were prepared by the US State Department and other state institutions of the United States and distributed, after being approved.
Demonization of the enemy can be much easier to conduct if the enemy is personalized in one man, such as Kaiser Wilhelm II, who was demonized by the Russian popular media during the First World War.
I hold it to a sign of great prudence in men to refrain alike from threats and from the use of insulting language, for neither of these things deprives the enemy of his power, but the first puts him more on his guard, while the other intensifies his hatred of you and makes him more industrious in devising means to harm you.
The strategy of demonization of the enemy unavoidably leads to a vicious cycle of atrocities, which was elaborated by many authors including Carl von Clausewitz. Demonization of the enemy makes diplomatic solution impossible and inevitably leads into the war or worsening of relations. Depicting the enemy as particularly evil inspires feelings that make killings more easy.
The portrayal of one's enemy as demonic has often led to the treatment of the whole population or political apparatus associated with the enemy group or leader as equally demonic. This also often results in a tendency to reduce an enemy's more complex motives to simple promotion of pure evil.
The Chinese revolutionary theorist Mao Zedong held that the demonization of oneself by the enemy was a good thing. He said, "It is still better if the enemy attacks us wildly and paints us as utterly black and without a single virtue; it demonstrates that we have not only drawn a clear line of demarcation between the enemy and ourselves but achieved a great deal in our work." (To Be Attacked by the Enemy Is Not a Bad Thing but a Good Thing (May 26, 1939)) 
...the demonization or dehumanization of the enemy...
State propaganda models are tactical strategies that employ enemy demonization techniques. The state promotes the idea that the threat (that is, tangible or intangible) is an evil aggressor whose sole goal is the destruction of the status quo.
The oldest trick of the propagandist is to demonize and dehumanize the hated other or others and make the enemy a ...
It is a banal fact that political leaders of nations fighting wars habitually demonize the enemy.... Hellenic speakers who strive to demonize and conceptually alienate other Hellenes....
In an article published in The Guardian (4 October 2001), Philip Knightley points out: The way wars are reported in the western media follows a depressingly predictable pattern: stage one, the crisis; stage two, the demonisation of the enemy's leader, stage three, the demonization of enemy as individuals; and stage four, atrocities.
They included scenes of enemy demonization and flag-waving patriotism, much in the vein of documentaries being prepared within the State Department and other bodies.
When official doctrine and guidance demonize the enemy and play on soldiers' fears, atrocities become inevitable'. ... As Carl von Clausewitz noted in On War, when either side in a conflict adopts such a strategy, demonization inevitably followed by atrocities... and thus the vicious cycle of savage war endlessly repeats until one side ultimately prevails.
Demonisation... In other words, portraying the enemy as malicious and repulsive creates feelings that makes killings easier.
The tendency to portray one's enemy as so evil as to be demonic has several bad effects. One is that of treating the whole enemy population - or, less drastically, the whole of the enemy civil and political apparatus - as tainted with the same satanic brush as the leadership itself.