For an intro to the USSR, particularly the revolutionary period, you will want to read October by China Melville (although people do say he falls for propaganda narratives about how the USSR fares after the revolution, so you will want to read other sources for that info). For critical American history, Howard Zinn’s A People’s History of the United States is a classic starting point a lot of people read in high school or college. There’s also a more recent book called How to Hide an Empire by Daniel Immerwahr that would also serve as a good intro. I haven’t read these, but I’ve also heard that Against Empire and Blackshirts and Reds by Parenti are good intro level history books. If I’m not mistaken, all of these books are on the theory MEGA file posted on the daily megathreads. For podcasts, RevLeft radio!