Describe the most important major change from the political map of Europe in 1918-1919.

As a result of the First World War, new states appeared on the map of Europe. Some of them already existed once (Poland – from November 1918), others appeared for the first time in history (Czechoslovakia, Latvia, Estonia, Lithuania).
Austria and Hungary split up. Romania increased its territory at the expense of Transylvania, Bulgaria lost access to the Aegean Sea. Montenegro became part of Serbia and due to the annexation of part of the territory of the former Austro-Hungary, the kingdom of Serbs, Croats and Slovenes arose. Germany lost part of its territory to Poland.