من كتاب "الحضارة ومنغصاتها" لفرويد

There is an advantage, not to be undervalued, in the existence of smaller communities, through which the aggressive instinct can find an outlet in enmity towards those outside the group. It is always possible to unite considerable numbers of men in love towards one another, so long as there are still some remaining as objects for aggressive manifestations. I once interested myself in the peculiar fact that peoples whose territories are adjacent, and are otherwise closely related, are always at feud with and ridiculing each other, as, for instance, the Spaniards and the Portuguese, the North and South Germans, the English and the Scotch, and so on. I gave it the name of' narcissism in respect of minor differences, which does not do much to explain it. One can now see that it is a convenient and relatively harmless form of satisfaction for aggressive tendencies, through which cohesion amongst the members of a group is made easier.