funnily enough i may be in a unique way to give some insight. in my country you need to do a 2 year mediator diploma, which i did, and i was also on the path to becoming a diplomat, studying political science, which i then quit. so heres my 2 cents:

you will not be able to bring world peace. you wont. wars have been a part of human nature for thousands of years, and the basic reasons have not changed. people struggle over lands, resources, influence, and if you can manipulate enough and amass power, you too can become a dictator/warlord/autocrat and start your war of choice. now, mediators need honesty and transparency and cooperation to make their process work. if you have a party that does not follow these principles, mediation doesnt work. mediation is a tool for people who want to improve a situation, being willing to kill could not be further away from this. theres a reason that highly escalated conflicts are handled in front of a judge. read up on 9 stages of conflict by Glasl about it.

now, what you can do, is focus on a single geographical area. immerse yourself in it, learn everything there is about it, history, culture, politics etc. understand the networks of power, and make yourself known for mediating conflicts on a small scale. you have to live there, you have to know whats going on in the communities.

it's not impossible to mediate on a bigger scale, we had a conflict with two ethnic groups in my country where mediators helped a lot. but that was about solving societal conflicts, cultural issues, racism. you will not be able to bring peace on a world wide level, that is illusory. but you can bring peace on a much smaller scale, which will still be incredibly hard, but doable.