The big two erased countries from ww1 were the austro-Hungarian empire and the ottoman empire.

If you don't include the breaking up of empires, then I can only think of a few nation-states which stopped existing due to the World Wars- but they all exist again today.

After the First World War, Montenegro became part of the Kingdom of Yugoslavia, and became independent again in the 1990s during the breakup of Yugoslavia.

Estonia, Latvia, and Lithuania were invaded by the Soviet Union and incorporated as Soviet Republics in 1940, and did not regain independence until the breakup of the USSR.

Prussia is the first that comes to mind, and is probably the most powerful single country to vanish from the maps, at least in Europe. But you´ll find plenty of gone countries in old European maps.