If you're looking for Marxist reads, you can go to https://www.marxists.org/index-mobiles.htm

They have a LOT of free ebooks on the topic. They have works by Marx, Engels, Lenin, Trotsky, and many others. They have histories about the Russian Revolution like John Reed's ten days that shook the world, all kinds of books that have analyses of socialism, communism, and history. All the books are public domain, and this older. But its everything you could want about the earliest writings and analyses of Marxism. And you can read everything there for free.