Esperanto is a constructed auxiliary language (like Interlingua or Ido) initially developed by Dr. Ludovic Lazarus Zamenhof and first published in 1897 with possibly two million fluent speakers of the language, and a thousand native speakers. There is significant evidence that Esperanto is easy to learn, highly regular in orthography, and flexible in grammar. Esperanto has a notable presence in over a hundred countries, recognised in 1954 by UNESCO and the instruction of the Akademio Internacia de la Sciencoj in San Marino. Formed in 2004, the Europe - Democracy - Esperanto party has contested elections in favour of a united democratic Europe with Esperanto as universal second language. In 2009, the Brazilian Senate voted to include Esperanto as an option in state schools. On February 22, 2012, Google Translate added Esperanto.

Dr. Zamenhof's ideals were high; he was raised in Bia?ystok, in contemporary Poland, where Yiddish, Lithunian, Polish, German, and Belarusian was spoken by significant parts of the community. Believing that a great deal of the mistrust between different parts of the community were due to misunderstanding, in the most literal sense, he sought to create a common language.

We are not so naïve as some think of us; we do not believe that a neutral base will turn men into angels, but we do know that evil people will always be evil; but we believe that communication and knowledge based upon a natural tool will prevent at least the great quantity of brutality and crimes which happen not because of ill will, but simply because of lack of knowledge and oppression.
- Ludovic Lazarus Zamenhof (1905)

The Declaration of Boulogne established the fundamentals of the language. There were attempts for Neutral Moresnet, between Belgium and Germany, to adopt the language before the invasion by the Kingdom of Prussia and post-war annexation by Belgium. The language achieved a degree of popularity after the First World War, with a proposal for the League of Nations to adopt it as the working language (with the French using their veto against). The League in fact recommended that its member states include Esperanto in their educational curricula. During the 1920s, the Brazilian Ministry of Education used Esperanto for their international correspondence.

During the Spanish Civil War in the 1930s it was extremely popular among the international Republican forces, especially the anarchists. Association with internationalism, anarchism, and Zemehof's own Jewish heritage led to both the Nazi Germany and the Soviet Union to ban the language. Stalin notoriously condemned it as "the language of spies", perhaps inadvertently increasing its popularity. Hitler, unsurprisingly, saw it as part of an international Jewish conspiracy As long as the Jew has not become the master of the other peoples, he must speak their languages whether he likes it or not, but as soon as they became his slaves, they would all have to learn a universal language, so that by this additional means the Jews could more easily dominate them!".

The history of Esperanto has included not only harassment and disparagement, but also outright bans and persecutions. Esperanto has been viewed by various regimes as a "dangerous language" (which is the title of a very commendable work noted in the Bibliography): As early as 1895 the journal La Esperantisto was disallowed from entering tsarist Russia; in 1922 the teaching of Esperanto was banned from French schools; in 1935 the teaching of Esperanto (which had been an optional subject at "free schools") was prohibited in Germany; in 1936 Esperanto itself was banned in Germany and Portugal from the mid-30s onward, publications of SAT [World Langauge Association] along with anarchist publications could no longer enter the USSR. As Stalinist repression increased, the activities of the once strong Soviet Esperanto movement were subjected to ever greater limitations. In a swift move in 1937, many of the most active Esperantists were arrested and either shot or sent off to prison camps. Esperanto was from then on ostracised and strictly forbidden as a "product of bourgeois internationalism and cosmopolitanism"; starting in 1938, Esperanto was banned in all territories that had been occupied or annexed by Germany.

(From Will Firth, in "Esperanto and the International Language Problem, 1998)