Why do wars happen? Because either someone wants territory/possessions that someone else has (land grab), or because someone wants to control the behavior of someone else (power grab).
In both cases, it begins with a lack of respect for the sovereignty of others. Every individual and every state has the right to its own things and to determine its own destiny. Peace happens when people and nations are respected to be left to themselves to enjoy what's theirs and to make their own decisions.
The most curious thing to me is that a good number of those who call for "world peace" are the ones who least want to respect the property and decisions of others. They want access to the money of the rich via overbearing taxation and they want to coerce behavior into their vision of how it ought to be. Neither of which they have a right to do. Taking what doesn't belong to them and restricting the freedom of others to choose their own way angers people. And it should. Theft and coercion are wrong - evil, even.
Want world peace? As Gandhi said, "Be the change you want to see in the world." Leave others alone to keep what they earn and to live their own lives. Funny, but that's pretty much what was written into our country's Declaration of Independence.
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.When those who call for world peace preach a respect for the unalienable right of liberty and self-determinmation for everyone, I'll take them seriously. Otherwise, they're just despots in miniature, trying to grab what isn't theirs and bringing about anything but peace in the process.