I personally think that peace should be preserved as long as possible. War is not something that you just jump into. I agree with Sun Tzu's notion that the soldier that fights for, and succesfully preserves peace should be awarded more glory than the solder who demonstrates genius in combat.
If it must come to war, it will only be when all diplomacy has failed. Such is the honorable way to wage war. The objective should be to neutralize the belliegerence against your country. WMD's would be avoided. Misconduct (massacres, corruption, Geneva code violations) on the part of my soldiers would be met with austere punishment. My soldiers would be professional service men, as opposed to government sanctioned thugs.
When occupying the country I would make some changes to the government, but I would try to give the populace as much free-reign over installing it as possible. Maximum courtesy would be in order amongst my troops, so as to deter the motivation for an insurgency.
blah, i'm bored.