Sadism: pleasure derived from the misfortunes of others or from causing others pain or misery.
The term 'sadism' is derived from the Marquis de Sade, who much exulted in sexual pleasure derived from the infliction of pain and of cruelty to others, and who wrote many books in praise of sadism, especially in the defined sexual sense.
When sadism is defined without necessary involvement of sexual pleasure, but in effect as the human-all-too-human joys derived from malice, it may be seen that sadism, thus defined, accounts for many human acts, especially against those whom the perpetrators dislike, consider as enemies, or believe to be inferior.
Indeed, there is much more sadism in human beings than most are willing to admit: Very many people derive much pleasure from being in positions of power and by hurting, denigrating, demeaning or displeasing others. It probably does not arouse most of them sexually, but they wouldn't do it if it did not please them. And this kind of pleasure seems to be one of the strongest motivators of those who desire to be boss: To let others feel they are inferior.
"We never hurt each other but by error or by malice."
(Sir Robert Chambers, possibly inspired by Dr. Johnson)
Together with stupidity, sadism explains two famous and mostly correct observations on history:
"History is little else but the register of the crimes, follies and misfortunes of mankind"
"Presque toute l'Histoire n'est qu'une suite d'horreurs."
For clearly most of the harm that human beings have done to human beings - millions upon millions killed, tortured, raped, exploited, starved, persecuted - was done on purpose, and willingly, and for the noblest sounding moral pretexts.
Accordingly, this 'human-all-too-human' desire to hurt, harm, demean, denigrate, abuse or exploit others is one of the normally unacknowledged forces of history, as is stupidity.
It is probably the normal human reaction to personal unhappiness: Make others suffer at least as much as one does oneself; demean those who seem better of than oneself, if one can do so without danger to oneself; and take vengeance for one's own pains, miseries and disappointments by wrecking even more of the same on the supposed enemies of one's society, or on social deviants or dissidents, since then one also gains moral credits easily, with the majority of one's peers.