Why can't we achieve world peace?

Why Can't We Achieve World Peace?

1. Why do conflicts happen?
2. Why can't people get along?
3. Who has attempted world peace and why it failed?

I already know that the world is barracaded by hate and greed. However, there is a glimmer of light that will shine down on it. I know that if there's not a war here than there's a war over there. That our world mostly consists of leaders that have serious trust issues, and have motives lead by greed. I know that treaties are very hard to come by and if there's a war, than there has to be a victor that rises up against it.