Esperanto was developed in the late 1870s and early 1880s by Dr. Ludovic Lazarus Zamenhof, a Jewish ophthalmologist from Bialystok, at the time part of the Russian Empire. According to Zamenhof, he created this language to foster harmony between people from different countries. After some ten years of development, which Zamenhof spent translating literature into Esperanto as well as writing original prose and verse, the first book of Esperanto grammar was published in Warsaw in July 1887. The number of speakers grew rapidly over the next few decades, at first primarily in the Russian Empire and Eastern Europe, then in Western Europe, the Americas, China, and Japan. In the early years, speakers of Esperanto kept in contact primarily through correspondence and periodicals, but in 1905 the first world congress of Esperanto speakers was held in Boulogne-sur-Mer, France. Since then world congresses have been held in different countries every year, except during the two World Wars. Since the Second World War, they have been attended by an average of over 2,000 and up to 6,000 people. As a potential vehicle for international understanding, Esperanto attracted the suspicion of many totalitarian states. In Germany, there was additional motivation to persecute Esperanto because Zamenhof was Jewish. In his work, Mein Kampf, Hitler mentioned Esperanto as an example of a language that would be used by an International Jewish Conspiracy once they achieved world domination. Esperantists were executed during the Holocaust, with Zamenhof's family in particular singled out for execution. It has continued to be used but no country has made it their official language.
From the description of Washington State Library's collection of L.L. Zamenhof letters and pamphlets, 1909. (Washington State Library, Office of Secretary of State). WorldCat record id: 433097046