Inside prison walls He wrote Epistles to all the kings and rulers of nations, summoning them to arbitration and universal peace. Some of the kings received His words with disdain and contempt. One of these was the Sultan of the Ottoman kingdom. Napoleon III of France did not reply. A second Epistle was addressed to him. It stated, "I have written you an Epistle before this, summoning you to the Cause of God, but you are of the heedless. You have proclaimed that you were the defender of the oppressed; now it hath become evident that you are not. Nor are you kind to your own suffering and oppressed people. Your actions are contrary to your own interests, and your kingly pride must fall. Because of your arrogance God shortly will destroy your sovereignty. France will flee away from you, and you will be overwhelmed by a great conquest. There will be lamentation and mourning, women bemoaning the loss of their sons." This arraignment of Napoleon III was published and spread.
Read it and consider: one prisoner, single and solitary, without assistant or defender, a foreigner and stranger imprisoned in the fortress of 'Akká, writing such letters to the Emperor of France and Sultan of Turkey. Reflect upon this: how Bahá'u'lláh upraised the standard of His Cause in prison. Refer to history. It is without parallel. No such thing has happened before that time nor since -- a prisoner and an exile advancing His Cause and spreading His teachings broadcast so that eventually He became powerful enough to conquer the very king who banished Him.
(‘Abdu’l-Baha, from a talk, 'The Promulgation of Universal Peace')