Politics, Places and Concepts Involving the Word "Country"
One of the more common uses of the word country, and perhaps the one that first comes to mind for English speakers when they think of country, is in the geo-political sense. The most generic Spanish word for this concept is país. The word nación tends to be used when the notion of country takes on a connotation of political organization.
España es un país muy montañoso (Spain is a very mountainous country).
¿De cuál país vino Ud.? (What country are you from?)
Ésta es una nación de leyes (This is a country of laws).
When one is speaking of one's country in a patriotic sense, the word to use is patria. It is found in such expressions as fiestas patrias, which means national holidays, because such holidays (generally known as días festivos) create a sense of cultural unity via the myths they perpetuate and culturally defining events they recall. The word patria has the same feel in Spanish as homeland or fatherland has in English. Unfortunately, fatherland was tainted by Nazi propaganda and so the English word isn't used as much anymore.
Muchos han muerto por su patria (Many have died for their country).
When speaking of country as the opposite of city, then campo is used. By the way, it is also a common surname in the Spanish-speaking world.
Nos mudamos al campo para evitar los ruidos y el crimen de la ciudad (We moved to the country to avoid the noise and crime of the city).
¿Has visto al Sr. Campo? (Have you seen Mr. Campo?)
In passing, the Mexican equivalent of country-western music is called música ranchera. A rancho is a farm, of course.
When one is speaking of the earth, dirt, soil -- or even the name of the planet we live on, then tierra is used. When it refers to the name of the planet, it is capitalized, as are the names of the other planets. It can also be used figuratively or poetically to speak of one's roots or place of origin.
Es malo para la tierra usar muchos químicos (It's bad for the earth/soil/dirt to use a lot of chemicals).
Después de la Tierra, Marte parece ser un planeta que pueda sostener la vida (After the Earth, Mars seems to be a planet that might sustain life).
Esta tierra es donde nací y donde he de morir (This land is where I was born and where I will die).
When speaking of a parcel of land, the terrain or its contours, the word terreno is used.
As a verb, as in to land an airplane, the word to use is aterrizar.