What is the phrase "Serving the country in War and Peace" in Latin? I need a translation for a novel I'm writing.
"In war and peace" would literally be in bello et in pace. However, there are a number of slightly more fancy idiomatic expressions for this idea (as was discussed in this question a while ago). By far the most common of these is domi militiaeque, which means: "at home and in military service."
(I am somewhat partial to the alternative armatus togatusque, which is a nice metaphor, but that could be problematic in a number of ways: the absurdity of the idea of, say, a modern politician wearing a toga, or the problem that it refers only to men -- women wearing togas was associated with prostitution.)
For "country" I would say res publica, which refers to the state, and is of course the root of the word "republic." Another possibility would be civitas, which more stresses the community of citizens (comes perhaps closer to "serving the people").
For "serving" I choose navare. Servire would also be possible, but more emphasises the submissive position of a servant.
Combining it all, we get:
Domi militiaeque rem publicam navare
Note: This is the infinitive form. You might want to choose another verb form depending on context, e.g. as a motto for an institution: navemus.
Sebastian's translation is solid and straightforward, but I'll offer a suggestion from a different angle. Why not try an existing Latin phrase?
Horace Odes 3.2.13 captures half of the sentiment sweetly:
Dulce et decorum est pro patria mori
It is sweet and proper to die for one's country.
You could add the verb vivere ("to live"), which although it would ruin the poetry, would capture your meaning well enough, I believe.
Dulce et decorum est pro patria mori at vivere.
Wikipedia says that a nineteenth century variant using vivere was actually used (by whom? how common? it is unsourced):
Dulce et decorum est pro patria mori, sed dulcius pro patria vivere.
It is sweet and proper to die for one's country, but sweeter [still] to live for it.
Perhaps your book demands a more straightforward translation, but I think it would be an interesting choice to use it somehow, with the added bonus of a recognizable allusion.