Short answers, pulled from the story.
The Great European Plain stretches from the Pyrenees mountains to the Russian Ural Mountains. This vast landform covers parts of Belgium, the Netherlands, Germany, Denmark, Poland, Lithuania, Latvia, Estonia, Finland, Belarus, Ukraine, Moldova, Romania, Bulgaria, and Kazakhstan.
Many important rivers cut through these plains like the Loire, Rhine, and Vistula in the west. Northern Dvina and Daugava flow northwards across East Europe and Russia while the Volga, the Don, and the Dnieper flow southwards out of European Russia.
One of the last large remnants of this primeval forest straddles the border between Belarus and Poland today. The European plain was once largely covered by forest before human settlement caused deforestation.
Large uninterrupted flatland provides very little geographic protection against invasion because armies found relatively easy access to neighboring countries across open space. France was invaded three times through the plain during that period and two of those successful occupations resulted in foreign control over the country.
The land supports dense populations and complex infrastructure networks while industrial zones cluster along river systems connecting major cities. Modern economies rely on the fertile soil and accessible waterways for growth and renewable energy production occurs at major centers throughout the territory.