I'd recommend The Diary of a Young Girl, the diary written by Anne Frank, a Jewish girl who hid from the Nazis during the Second World War. I'm a history teacher at a secondary school in Istanbul, and I've given this book to many students.
The diary covers about two years, when Anne, her family and four other people lived secretly in some hidden rooms behind a business in Amsterdam. Anne started writing when she was thirteen. She writes about being bored, arguing with her mother, falling for a boy who's also in hiding, and her dreams of becoming a writer. At the same time, there's constant fear of being discovered. The diary stops suddenly when they're found and arrested, and Anne died in a camp a few months before the war ended.
I first read it at fifteen, in Turkish, because my own history teacher gave it to me, and it was the first book that made history feel real.
There are a few reasons I think every teenager should read it. Firstly, it's written by a teenager, so young readers immediately recognise themselves. Anne complains about her parents and worries about her looks, exactly like my students do, and that makes the tragedy hit much harder. Secondly, it teaches history in a human way. Students often see wars as dates and numbers, but here it's one funny, clever girl, which makes them understand what prejudice can lead to. And finally, it's simply beautifully written. Anne was very honest and very observant, and many students tell me it inspired them to keep a diary of their own.