Bahá’u’lláh addresses the “kings of the earth”

O kings of the earth! Give ear unto the Voice of God, calling from this sublime, this fruit-laden Tree, that hath sprung out of the Crimson Hill, upon the holy Plain, intoning the words: ‘There is none other God but He, the Mighty, the All-Powerful, the All-Wise.’... Fear God, O concourse of kings, and suffer not yourselves to be deprived of this most sublime grace. Fling away, then, the things ye possess, and take fast hold on the Handle of God, the Exalted, the Great. Set your hearts towards the Face of God, and abandon that which your desires have bidden you to follow, and be not of those who perish. 

- Baha’u’llah  (Quoted by Shoghi Effendi, ‘The Promised Day Is Come’)

People who were addressed in the Súriy-i-Mulúk (Súrih of Kings)

In a memorable Tablet, designated as the Súriy-i-Mulúk (Súrih of Kings) in which

• the Sultán himself and
• his ministers, and the kings of Christendom, and
• the French and Persian Ambassadors accredited to the Sublime Porte, and
• the Muslim ecclesiastical leaders in Constantinople, and
• its wise men and its inhabitants, and
• the people of Persia, and
• the philosophers of the world

have been specifically addressed and admonished, He thus directs His words to the entire company of the monarchs of East and West: 

- Shoghi Effendi  (‘The Promised Day Is Come’) 

“Bahá’u’lláh has not restricted the delivery of His Message to a few individual sovereigns”

It should be borne in mind, however, that Bahá’u’lláh has not restricted the delivery of His Message to a few individual sovereigns, however potent the scepters they severally wielded, and however vast the dominions which they ruled. All the kings of the earth have been collectively addressed by His Pen, appealed to, and warned, at a time when the star of His Revelation was mounting its zenith, and whilst He lay a prisoner in the hands, and in the vicinity of the court, of His royal enemy. 

- Shoghi Effendi  (‘The Promised Day Is Come’)

“most of the preeminent embodiments of power and of sovereignty in His day became, one by one, the object of Bahá’u’lláh’s special attention, and were made to sustain, in varying degrees, the weight of the force communicated by His appeals and warnings”

• The Emperor of the French, the most powerful ruler of his day on the European continent, Napoleon III;
• Pope Pius IX, the supreme head of the highest church in Christendom, and wielder of the scepter of both temporal and spiritual authority;
• the omnipotent Czar of the vast Russian Empire, Alexander II;
• the renowned Queen Victoria, whose sovereignty extended over the greatest political combination the world has witnessed;
• William I, the conqueror of Napoleon III, King of Prussia and the newly acclaimed monarch of a unified Germany;
• Francis Joseph, the autocratic king-emperor of the Austro-Hungarian monarchy, the heir of the far-famed Holy Roman Empire;
• the tyrannical ‘Abdu’l-‘Azíz, the embodiment of the concentrated power vested in the Sultanate and the Caliphate;
• the notorious Násiri’d-Dín Sháh, the despotic ruler of Persia and the mightiest potentate of Shí’ih Islám—

in a word, most of the preeminent embodiments of power and of sovereignty in His day became, one by one, the object of Bahá’u’lláh’s special attention, and were made to sustain, in varying degrees, the weight of the force communicated by His appeals and warnings. 

- Shoghi Effendi  (‘The Promised Day Is Come’)