John Quincy Adams on Islam:

In the seventh century of the Christian era, a wandering Arab of the lineage of Hagar, the Egyptian, [ Editor’s Note: Mohammed] combining the powers of transcendent genius, with the preternatural energy of a fanatic, and the fraudulent spirit of an impostor, proclaimed himself as a messenger from Heaven, and spread desolation and delusion over an extensive portion of the earth. Adopting from the sublime conception of the Mosaic law, the doctrine of one omnipotent God; he connected indissolubly with it, the audacious falsehood, that he was himself his prophet and apostle. Adopting from the new Revelation of Jesus, the faith and hope of immortal life, and of future retribution, he humbled it to the dust, by adapting all the rewards and sanctions of his religion to the gratification of the sexual passion.

He poisoned the sources of human felicity at the fountain, by degrading the condition of the female sex, and the allowance of polygamy; and he declared undistinguishing and exterminating war, as a part of his religion, against all the rest of mankind. THE ESSENCE OF HIS DOCTRINE WAS VIOLENCE AND LUST: TO EXALT THE BRUTAL OVER THE SPIRITUAL PART OF HUMAN NATURE [capitals in original].

Between these two religions, thus contrasted in their characters, a war of twelve hundred years has already raged. That war is yet flagrant; nor can it cease but by the extinction of that imposture, which has been permitted by Providence to prolong the degeneracy of man. While the merciless and dissolute dogmas of the false prophet shall furnish motives to human action, there can never be peace upon earth, and good will towards men. The hand of Ishmael will be against every man, and every man’s hand against him. It is, indeed, amongst the mysterious dealings of God, that this delusion should have been suffered for so many ages, and during so many generations of human kind, to prevail over the doctrines of the meek and peaceful and benevolent Jesus…

The precept of the koran is, perpetual war against all who deny, that Mahomet is the prophet of God. The vanquished may purchase their lives, by the payment of tribute; the victorious may be appeased by a false and delusive promise of peace; and the faithful follower of the prophet, may submit to the imperious necessities of defeat: but the command to propagate the Moslem creed by the sword is always obligatory, when it can be made effective. The commands of the prophet may be performed alike, by fraud, or by force.

(Capitals in original)

—John Quincy Adams, “Christianity—Islamism.” “Unsigned essays dealing with the Russo-Turkish War, and on Greece,” originally published in The American Annual Register for 1827–1829 (New York, 1830).