Do you believe warfare should be used to gain more territory and add to the prestige of your country?

No.  Initially you gain riches from the resources found in those territories and yes you extend your sphere of influence farther and with it your power increases.  Still.  Eventually there will come a time when the people of those lands will rise up and demand independence.  Through peaceful means at first but if not, they will resort to conflict that will be costly on both sides.  Then it will all boil down to whether you want to hold on or release your hold on that territory. If you hold on, they will more determined to break free from that hold. That you gain something through war means you will lose it through war if you don't want to let go.