The League Against Imperialism was a group of people who joined together to protest against other people or countries trying to take over or control other countries or people. You know how when you play with your toys, you don't like it when someone tries to take them away from you without asking? Well, the people in the League Against Imperialism felt the same way about countries trying to take over other countries.
They believed that every country and culture should be respected and allowed to make decisions for themselves, without any other country or people interfering. Just like how your parents or guardians may let you make some decisions about what you want to eat or wear, even if they haven't made those same choices before.
The League Against Imperialism wanted to make sure that everyone had a voice and that no one country or group was more important than the others. They believed that each group and country had unique things to offer and that by working together, everyone could learn from each other and grow. It was like having a big family, where everyone is different but still loves each other and helps each other out.