The only legal cause of slavery in Islâm is prisonership of war or birth from slave parents. The captivity of enemies of Islâm has not at all necessarily the effect of enslaving them; for the competent authorities may dispose of them in any other way, also in the way prescribed by modern international law or custom. In proportion to the realization of the political ideal of Islâm the number of its enemies must diminish and the possibilities of enslaving men must consequently decrease. Setting slaves free is one of the most meritorious pious works, and, at the same time, the regular atonement for certain transgressions of the sacred law. So, according to Mohammedan principles, slavery is an institution destined to disappear. When, in the last century, Mohammedan princes signed international treaties for the suppression of slavery, from their point of view this was a premature anticipation of a future political and social development--a step which they felt obliged to take out of consideration for the great powers. In Arabia, every effort of the Turkish Government to put such international agreements into execution has thus far given rise to popular sedition against the Ottoman authority. Therefore, the promulgation of decrees of abolition was stopped; and slavery continued to exist. The import of slaves from Africa has, in fact, considerably diminished; but I am not quite sure of the proportional increase of the liberty which the natives of that continent enjoy at home. Slavery as well as polygamy is in a certain sense to Mohammedans a sacred institution, being incorporated in their Holy Law; but the practice of neither of the two institutions is indispensable to the integrity of Islâm. All those antiquated institutions, if considered from the point of view of modern international intercourse, are only a trifle in comparison with the legal prescriptions of Islâm concerning the attitude of the Mohammedan community against the parts of the world not yet subject to its authority, "the Abode of War" as they are technically called. It is a principal duty of the Khalif, or of the chiefs considered as his substitutes in different countries, to avail themselves of every opportunity to extend by force the dominion of Allah and His Messenger. With unsubdued unbelievers _peace_ is not _allowed_; a _truce_ for a period not exceeding ten years may be concluded if the interest of Islâm requires it.