Positive thinking can be subjective based on people perspective. Some people decided to not get into others problem, even they are related, because they think it's the best. Let say some people did bad things as they mean as jokes to other people and they don't realize it. The people who is hurt then feel sad, and that people think positively, that they are not the one who cause the sadness. I think positive thinking has a lot of definition based on condition and perspective. It's really hard to declare one clear definition of positive thinking, realizing people comes from a lot of different backgrounds. How can the world be peaceful? Relating to international relation, peace than can actually happen is when there is no war, which refer to negative peace. In this case, There are still problems that can cause conflict, and people doesn't really feel safe. The concept of positive peace like perpetual peace mentioned, is kind of too naive. How state act, decide it's foreign policy, prioritize its interest, make this perpetual peace can not be achieved.
To me, positive thinking is very illusive. It means different things to different people given their differing backgrounds and socialization.
To the second part of your question: whether it is possible to produce positive thinking in all of humanity, I say that it is not possible given our differing interpretations of what might constitute the 'positive'. If positive thinking is something that is reproduceable in all of humanity, then the question of conflict, war would not have arise. The UN can be conceived of as part of positive thinking but was it able to produce positive thinking among all people and nations through its collective security apparatus?