When did Baha'u'llah write "the earth is but one country and mankind its citizens" ?

Hello phlatphrog,

This passage comes originally from the Lawh-i-Maqsúd.

"Tablets of Bahá?u?lláh Revealed After the Kitáb-i-Aqdas:
Lawh-i-Maqsúd (Tablet of Maqsúd)" [p. 167]
Bahá'í Reference Library
http://reference.bahai.org/en/t/b/TB/tb-12.html#pg167

The Lawh-i-Maqsúd was revealed on January 20, 1882, and was apparently
written on December 31, 1881.

"Lawh-i-Maqsúd: Letter from the Universal House of Justice; excerpt
from Juan Cole's Modernity and Millennium"
Bahá'í Library Online
http://bahai-library.com/resources/tablets-notes/lawh-maqsud/notes.html

- justaskscott


Search strategy --

I started with search for:

"the earth is but one country and mankind its citizens"

I expanded this search phrase to include the word that appears prior
to the original phrase ("world"); then expanded the search further to
include the word "proclamation" as an additional term; and eventually
browsed and searched the useful sites indicated above to find the
answer.