Was there a tragedy that happened during the authors lifetime that motivated him to write about this topic?

Yes, Harper Lee drew inspiration from her own experiences growing up in the segregated South and witnessing racial injustices and prejudices which influenced her to write about such themes in "To Kill a Mockingbird." Additionally, the Scottsboro Boys case, an infamous miscarriage of justice involving nine African American teenagers falsely accused of rape in Alabama, likely had an impact on her writing as well.