This plain is situated in the Southern part of Romania and is called Cîmpia Română (the Romanian plain).
In the southern and eastern parts of the country is the Great Hungarian Plain (also known as Great Alföld, Alföld, or Pannonian Plain). The associated steppe biome is called the puszta (or pusta), which is Hungarian for plains.
The Plain of Wallachia is located in the country of Romania.
Romania has approx. 35 % from the area as plains.
Romania.
Romania
Bucharest is the capital and largest city of Romania.
The largest plain in Europe is known as either the European Plain or the Great European Plain.
The biggest city in Romania is Bucharest.
Romania has an area of 238 391 km2 and is 82nd in the world.
That should be Wallachia, I believe, and it would be Romania.
Romania
West Siberian Plain