1. geography (noun):

in political terms, the study of how the Earth’s surface, including mountains, deserts, plains, oceans, etcetera, along with its climate, resources, and populations, affect the relationships between nations

“But geography, and the history of how nations have established themselves within that geography, remains crucial to our understanding of the world today and to our future.” (Introduction, page 7)

2. North European Plane (proper noun):

a broad, flat region that stretches east from northern France and Germany through Poland and into Russia, and provides a corridor for invading armies

“In the past five-hundred years they have been invaded several times from the west […] the Russians were fighting on average in or around the North European Plain once every thirty-three years.” (Chapter 1, page 13)

3. Soviet Union (proper noun):

also called the USSR, or United Soviet Socialist Republic, from 1922 to 1991 a large nation that stretched from eastern Europe across Siberia to the Pacific Ocean, most of whose land and population is now part of Russia

“In the twentieth century, Communist Russia created the Soviet Union. Behind the rhetoric of ‘Workers of the World Unite’ the USSR was simply the Russian Empire writ large.