Whatever it may be in life, people and countries get frustrated when they cannot get their way, so enemies are created, so that people that you don't respect or don't want to respect, as well as people that are a constant inconvenience to the established order to have around, and so on and so forth, are effectively demonized by displacing their innate humanity and replacing it with something that makes these targets appear to be something far less than human.
For instance, in today's world, most countries aren't really war mongers, that is to say, it isn't easy convincing one's own population that you need to attack another country in order to take their land, their resources, and subjugate their people, when legitimate avenues such as trade and cross-cultural exchanges are readily available, so the basic secret to whip up support for any war, is to justify it by demonstrating that the supposed enemy are savages, or heretics, and typically by pointing out that some sort of isolated attack, that took the lives of a few of your citizens, or violated your border, or insulted whomever, necessitates full-on righteous retribution. In addition, you pick on something about them which is physical, religious, or cultural, that your enemy seems to have an abundance of, and effectively ridicule it to the nth degree, preferably over a long or relentless period of time, that dehumanizes the enemy, making them appear to be animalistic, or uncivilized, and so on and so forth, so that you can more easily whip up the patriotic waves of justified reprisal against an intolerant and intractable enemy of infidels, savages, or outlaws.
Then too, this type of demonization is often used internally within a country to isolate and attack specific races, or creeds, or color, of which usually most of these are relatively easy to target, because they either physically look different from the favored people, or dress differently, or have different behavioral patterns, so that the ruling class can intently focus on those differences, declare those differences to be a real and present danger to the ruling class, and because these people are different and cannot be assimilated that they must therefore of necessity be eliminated, marginalized, or banished.
In addition, there are those that are severely handicapped, or are very aged, of which the utility to the country of these people are infinitesimally small, so that it becomes public policy, that for the good of the state, for the good of the majority, that these people must be isolated and made to feel guilty for their being alive, made to feel useless, unwanted, unneeded, and undesired, while at the same time providing these people an easy avenue of voluntary surrender to euthanasia or similar.
All of the above, follow the same basic footprint, which is to take something that is obviously human, and make them appear to the credulous public as far less than human, less valued, or of no value, and rather than to recognize that all have inalienable rights as gifted to us by our Creator, of which His human creations come to us in a variety of sizes, shapes, and beliefs; instead we segregate and attack those that we wish to dismiss, so as to wrongfully take from them what is theirs, to make enemies of those that could be our friends, and to unnecessarily polarize situations that could be harmonized, for it is always far easier and far more palatable to take care of any dirty business, if we first are convinced, that our opponents are not worthy of our agape love or humanitarian consideration.