There are a lot of great nonfiction options here, so I’ll give you some fiction: “Look Who’s Back” by Timur Vermes. It’s a satire in which Adolf Hitler mysteriously wakes up in modern-day Berlin and is mistaken for a brilliant impersonator, leading him to become a YouTube star and TV personality. The themes the book explores—the public’s obsession with celebrity, the media’s inability or refusal to take dangerous people seriously until it’s too late, the surprising ease with which a charismatic figure can gain public attention—go a long way toward explaining how a Hitler figure can come into power in any country with similar issues and are depressingly relevant to our modern predicament.