I'd start by doing voluntary work and helping the poor because I can't stop all the wars alone. Maybe, if people lived in better conditions, the wars would stop ! =P
I'd give food, clothes and all the items they need . For that I'd ask for help to my friends and parents.I try not to pollute the streets and rivers, I also try recycling things and taking care of the animals .I think If you can't do everything, do everything you can ! Maybe we'll have a better world!