Step 1: Recall the definition of a noun.
A noun names a:
person,
place,
thing,
event or idea.
Step 2: Analyse each option. and — a conjunction, not a noun.
were — a verb (past tense of \emph{be}).
during — a preposition.
war — names an event; hence a noun.
Step 3: Identify the correct noun.
The word war functions as a noun in the sentence.
Hence, the correct answer is
\[
\boxed{\text{war}}
\]