Slaughterhouse Five

Having read most of Slaughterhouse Five, I can say, without a doubt, that I am completely confused on how mixing together history and strange aliens from another planet can even remotely work. I'd normally think nothing that combines history and aliens would be able to work, but apparently it works perfectly fine in this book. How does putting something serious and completely fictional manage to pass? My brain is telling me that shouldn't be able to work but having read the book, but there's just no issue with the book in doing so. Moving on from that strange combination, I was also really surprised at the book having three titles. I've never seen a book with more than one title before, probably because I don't read that many books, but three titles seems a bit excessive to me. Don't get me wrong, I don't have anything against a book having multiple titles, it just seems strange to me. Overall though the story really captivated me and I'm definitely going to read this book again in my free time.