I will talk about 2 of the Kings and Queen of His time, namely, Napoleon III and Queen Victoria.

You should note, that Baha’u’llah came to fulfil the prophecies of the past Religions such as the Return of Christ, and the Promised One, to lead humanity to all Truth.

So, it was imperative that Baha’u’llah wrote to kings and rulers of His time to inform them of the time they were living and the will of God for today.

Most of them took His message as heresy and lunatic.

i.e., Baha’u’llah said to Napoleon III that he needs to turn to the Will of God and Baha’u’llah said a lot of things about His station and His mission to bring about the Most Great Peace.

You know what Napoleon III responded to Baha’u’llah? He said, “If this man is God, I am two Gods.”

Shortly after in about 3 years or so, approximately, Napoleon’s kingdom fell

Beginning in 1867 in Adrianople and continuing later in ‘Akká, Bahá’u’lláh wrote to the kings and rulers of the world,

Read Baha’u’llah’s Summons of the Lord of Hosts where He writes to all of the Kings and Rulers of His time:

http://www.bahai.org/library/authoritative-texts/bahaullah/summons-lord-hosts/

Baha’u’llah wrote back to Napoleon III
“For what thou hast done, thy kingdom shall be thrown into confusion, and thine empire shall pass from thine hands, as a punishment for that which thou hast wrought. 21 Then wilt thou know how thou hast plainly erred. Commotions shall seize all the people in that land, unless thou arisest to help this Cause.”
http://reference.bahai.org/en/t/b/PB/pb-6.html

Credited Video Clips:

Queen Victoria (1819-1901) – Pt 1/3

The Franco-Prussian…

Songs By dyalla – Uptown and Joakim Karud – Great Days