Russell, Bertrand -- Education and the Social Order [Education and the Modern World], ch. 1 “The Individual vs. the Citizen” (1932)

If you wish a man to commit some abominable crime, from which he would naturally recoil in horror, you first teach him loyalty to a gang of arch-criminals, and then make his crime appear to him as exemplifying the virtue of loyalty. Of this process, patriotism is the most perfect instance.