I am re-reading W.E.B. Du Bois' The Souls of Black Folk for my social theory class.
In that book, published at the dawn of the previous century, he famously argues that "the problem of the twentieth century is the problem of the color line." I had read this argument before as Du Bois correctly discerning the long hard civil rights struggle in the United States.
What I had not appreciated until this reading was that he clearly meant the entire global question of the interaction of the white and non-white races. He had in mind European colonialism just as much as American race relations.
In making my social theory class I am trying to pick pre-eminently transformative books. One good test is whether the book itself, and not just the author, has its own Wikipedia page.
The Souls of Black Folk was prescient not just about civil rights in America, but about colonialism and post-colonialism all over the world.