Country

You're probably seeing a trend here but yes a country is a collection of cities. We could go on to star systems and galaxies, but they essentially function similarly to countries in a story context. Large scale terrain is usually only important if travel or battle is a large part of the plot. Rarely are the grand affairs of a country important unless there is a state of war. When the character is integral to the affairs of the state is when the audience needs to start knowing about the politics and schemes and what not.

Strategy and tactics are likely to be misunderstood by both yourself and the reader unless some hard facts about terrain are established.

The Eastonians arrive at the barren dust bowl of Cottonmouth Pass only to find the Westerrans already controlled the canyon rim. "A minor disadvantage, they won't hold long in this desert once they learn 32nd and 48th platoons have circled round to cut off their supplies."

Two sentences sum up that there is a battle, who's fighting in it, some sense of the army size, and what the terrain is like.

In a lengthier series it may be necessary to include some form of a map, showing major landmarks and cities that the characters will travel through/fight at/stop for tea the detail on that is up to your discretion.