This is an opinionated question, but here are some points that may help you create your own answer to this question.
➜ Different societies are currently changing and evolving. We all want to grow stronger, expand, etc. This can lead to battles over land, resources, or more. There will always be something to fight over, creating global peace would mean deciding not to.
➜ Global peace, or world peace, is frequently defined as the absence of conflict among and within nations. There are nearly 8 billion people who live in the world. Humans are commonly emotional and we often get into fights or arguments. This makes global peace very difficult.
➜ We sometimes forget our history. This leads to repeating past mistakes, like the devastating world wars.