Dune by Frank Herbert, it does a good job taking problems with our world and framing them in a fictional context. Like the struggle of the Fremen and unregulated capitalism.
The Underground Railroad this was required reading when I was in school. It's quite significant and about the struggles of slavery in America.
The Penguin Book of Japanese Short Stories This collection of short stories tries to illustrate various morals and experiences. Like how the western world glossed over the struggles of Japanese people soon after the nuclear bombings.
The Satanic Verses This one is a hard sell, especially given the constraints you've set. Put bluntly it's a mockery of biblical texts, but it's highlighting the whimsical nature of religion and its chilling effects. People have been murdered over this book and I feel it wouldn't be fair to those who have died not to mention it here.