A year later, the Treaty of Versailles awarded Neutral Moresnet to Belgium, as from 10 January 1921, when it become the municipality of Kelmis.

After the demise of Napoleon's Empire, the Congress of Vienna of 1814–15 redrew the European map, intending to create a balance of power in Europe.

Both parties could agree on the larger part of the territory, as borders mostly followed older lines, but the district of Moresnet proved problematic, mainly because of a valuable zinc spar mine named Altenberg (German) or Vieille Montagne (French) located there.

[9] In December 1815, Dutch and Prussian representatives convened in nearby Aachen, and on 26 June 1816 a compromise was obtained, dividing the district of Moresnet into three parts.

The Napoleonic civil and penal codes, introduced during French rule, remained in force throughout the existence of Neutral Moresnet.

In 1859, Neutral Moresnet was granted a greater measure of self-administration by the installation of a municipal council of ten members.

[13] Life in Neutral Moresnet was dominated by the Vieille Montagne mining company, which not only was the major employer but also operated residences, shops, a hospital and a bank.

A downside to their special status was the fact that people from Neutral Moresnet were considered to be stateless and were not allowed a military of their own.

Perhaps in response, the next year Dr. Wilhelm Molly (1838–1919), the mine's chief medical doctor and an avid philatelist, tried to organise a local postal service with its own stamps.

[16] About 1900, Germany began a more aggressive policy concerning the territory and was accused of sabotage and obstructing the administrative process in order to force the issue.

The Moresnet casino operated with strict limitations, permitting no local resident to gamble, and no more than 20 people to gather at a time.

The venture was abandoned, however, when Kaiser Wilhelm II threatened to partition the territory or cede it to Belgium in order to end the gambling.

During 1908, Dr. Molly proposed making Neutral Moresnet the world's first Esperanto‑speaking state, named Amikejo ("friendship-place").

[18] A number of residents learned Esperanto and a rally was held in Kelmis to endorse the idea of Amikejo on 13 August 1908,[16] and a coat of arms was publicized.

On 4 August 1914, Germany invaded Belgium, initially leaving Neutral Moresnet as "an oasis in a desert of destruction".

It continues to exist as VMZINC, a part of Union Minière, the latter renamed in 2001 as Umicore, a global materials company.