Which of the two following sentences correctly uses "ours"? Is it correct to write, "Why fight a war that isn't ours?" or "Why fight a war that...

The href="http://alt-usage-english.org/excerpts/fxwheret.html">personal possesives
pronouns our and ours--the
possessive form variations of the personal plural pronoun we--never
use an apostrophe to indicate possessiveness. The reason is because of the word class
they belong to. The word class they belong to is that of personal
possessive pronouns. No personal possessive pronoun in English takes an
apostrophe to indicate its possessiveness. This is because the entire word is the
possessive form. There is no instance in which the word our or
ours is not a possessive. Since this is true, there is no need for
the redundancy of the possessive indicator 's. Other personal
possessive pronouns are his, its, whose, their, hers, ours,
yours, theirs. None of these personal possessive pronouns take
the possessive marker 's, because each entire word is the
possessive form and never used in any other
way.

Additionally, when personal pronouns are
written with apostrophes, they are
contractions of the pronoun plus a to
be or a to have word: it's (it +
is; it + has, as in it has got: it's got),
they're (they + are), who's (who + is; who +
has as in who has got: who's got).

In
contrast, indefinite href="http://www.english-grammar-revolution.com/list-of-pronouns.html">pronouns
like anybody, somebody, anyone, everybody, everyone, nobody, no one, one,
someone, do require the possessive marker to make them possessive. These
words are not personal possessive pronouns; they are indefinite pronouns for plural or
singular entities. To indicate possession associated with this class of word, the
possessive marker is required: anybody's, somebody's, anyone's, everybody's,
everyone's, nobody's, no one's, one's, someone's.