I’d suggest you to look for a guidebook on any of Marx’s works, or Engels. He’s right about many things, but he is a boring writer. Reading his stuff is tedious, especially without a guide. I see others recommend starting to learn about Marx from people after him, but I completely disagree that that’s a good place to start. Dictators, oppressors, and war crime deniers have nothing of value to say.
Nationalism is the stupidest thing humans have created regardless of who their propaganda affects and how.