To answer your questions directly:
Why we don't kill eachother - strict society control and punishment. It is scientifically proven that if a person is absolved of responsibility, over 95% of human population is fully capable of killing a fellow human being, even if that human is begging them in tears not to. Vast majority of the rest will stop VERY short of killing.
Why the major industrialized countries haven't gone to war with eachother - MAD. If you don't know that is, it stands for "Mutual Annihilation Doctrine". If you still have no clue, google it.
And as for the rest of the world - the current historical record for maintaining the longest peace in known history is in Roman hands - approximately 200 years of peace in their golden age. They achieved that becase their army was notorious for both its power and its extreme cruelty - in other words it exterted the same "control via fear of consequence" as the one I discussed above.
Western countries are constantly involved in the armed conflicts, from non-ending Israel vs Arab world, to bigger wars like Korea, Vietnam, Afghanistan, Yugoslavia and Iraq, and minor and far away (and usually more bloody percentage-wise) post colonial wars all over Africa and Asia. Just because you don't see thousands of raped teen girls on TV, or thousands of poor teen boys claming revenge over the bodies of their sisters doesn't mean that they don't exist.
Lastly, you would do good to note that the world "sort of" has a terrorism problem. I can assure you that only few of those, inspite of what Bush's administration loves to claim, are religious fanatics. Majority of these, as even a short research would show you, are kids from the enviroments that I talked about in my previous post. People like that don't have values that you are talking about - they live in "kill and enjoy life or be killed by the other kids competing for the same rights to rape and pillage" - world. Your post shows that you have as much understanding of that world as they have of yours. And there's at least as much of people like that as there are people in industrialized world, and probably more due to the fact that people in those countries breed like rabbits while industrialized nations' birth numbers are stalling.
All your assumtions so far are based on the fact that YOUR values are EVERYONE'S values. I honestly thought that most people, at least in Europe, would at least learn from the Bush's crusades that this is not so. Apparently I was wrong.
EDIT: and as for well-off people, they aren't all that better off. While they are indeed restricted by the society, should you read some things that you hear from the direction of the goold old USA, you'll notice that most people were all for Iraq war before and during the beginnig. Only when the hurt started to be laid on their side as well did they start questioning if it was right to invade another country. Superiority/inferiority complex and the need to show off is very powerful in western cultures and can cause just as much bloodshed. Also, you'll note that Yugoslavia wasn't all that poor either. We had ethnical tensions there however, and with Tito dead, it all started to slow head for the collapse that we had in the end.
And as for the particular form of warfare used here, this is a typical "we don't kill people, we fight a war" attitude that most combat pilots get. To them, killing is so impersonal, they often don't see themseves as killers, rather looking at themselves as some sort of warriors fighting "the enemy". And since all the enemy that they get to see is either an enemy plane, or enemy vehicles on a small grainy screen, they never get to experience the "knee-deep in blood" feeling.
Lastly, read up on Afghan conflict (the one in 70s, USSR vs CIA & mojahedeen fighters). Specifically at the accounts of veterans - I personally knew several. They range from insane gyus who spend the rest of their days in a hospital asking kids they killed for forgiveness (usually an assault helicopter's pilot/gunner) to stone cold killer types that can wring a neck of a kid of throwing a ball at their window (usually paratroopers and special forces). But average afghan war veterans are quite normal people with just slight psycological shifts due to traumas. And those are people that were effectively pulling the same shit as americans did in Vietnam, only with the difference that they were even more sexually "creative" as most russians tend to be.
