In the first place we should insist that if the immigrant who comes here in good faith becomes an American and assimilates himself to us, he shall be treated on an exact equality with everyone else, for it is an outrage to discriminate against any such man because of creed, or birthplace, or origin. But this is predicated upon the man’s becoming in very fact an American, and nothing but an American. If he tries to keep segregated with men of his own origin and separated from the rest of America, then he isn’t doing his part as an American. There can be no divided allegiance here. Any man who says he is an American, but something else also, isn’t an American at all. We have room for but one flag, the American flag, and this excludes the red flag, which symbolizes all wars against liberty and civilization, just as much as it excludes any foreign flag of a nation to which we are hostile. We have room for but one language here, and that is the English language, for we intend to see that the crucible turns our people out as Americans, of American nationality, and not as dwellers in a polyglot boarding-house; and we have room for but one sole loyalty, and that is loyalty to the American people.
Letter by Theodore Roosevelt (3 January 1919) to Charles Steward Davison, Chairman of the Board of Trustees of the American Defense Society. It was one of the last letters he wrote.