Peace
As much as it pains me to admit (and will most likely lead to my ridicule) at present or in the forseeable future there is no chance for world peace. I've realized there are mainly two reasons for this, class and religion. Scoff if you will but those are humanities greatest hurdles to world peace. Though even in a classless, religionless society race may still lead to some strife. Currently the class difference is great but it hasn't been violent so far but if the "lower" class organizes against the "upper" class it will be a very violent struggle. At the moment the main difference in classes is money, but over time that could change and the differences could and will grow greater if you world (America especially) continues on the path it is heading down. For example I have observed the so called upper class treating the lower class (be it a gas station attendant or some other "unskilled" person who performs a service for them) if not with disgust then with disdain. The "classer" isn't nearly as explosive as the religious "er" though. Throughout human history blood has been spilled often either in the name of "god" or against another religion specifically. The Crusades, The Salem Witch Trials, The Holocaust, the current Israel/Palestine conflict, and the continuing Islamic Jihad against the west are just a few examples.
As long as two or more religions exist with different idealogies the followers of the different religions will almost certainly clash at some point and probably very violently. All you have to do is study the past to back up these conclusions on a planet with a population of six billion plus with hundreds of nations (some with very old unsettled disputes) the idea that all of those nations and people can unite is laughable. No matter how many nations unite in peace there will always be groups such as Al-Qaeda, Hamas or even just someone such as Kim Jong-Il that will disagree with something or other.
Sad as it is true world peace is an illusion.