Which of the following statements is true regarding the growth of nationalism in the 19th century A.war and conflict were often used as vehicles to...

Of these possible answers that you offer, I would say that
the correct one is A -- wars and conflicts were often used as a way for nationalist
leaders to unite their people.

The most obvious examples of
this can be seen in Italy and Germany.  Both of these countries experienced nationalism
in the late 1800s.  They both used wars and conflicts to help the nationalism along.  In
time, the nationalism grew to a great enough extent that the two countries were actually
able to become single countries (they used to be split up into lots of little
countries).