Wikipedia is actually a decent resource to get started. Your story seems set: an oppressed people in a colony yearns for freedom. Congo under Belgian rule is a great reference to describe the horrors of colonialism. Describe it from the protagonist's point of view - what's their life like? What do they know about their colonizers, like, are there rumors about where they came from? Then look at various anticolonial struggles. Sankara is a magnificent template for The Chosen One. Once you set up the world and have started describing your protagonists life, your story starts writing itself.