Eh, I’m not sure I’d go so far as to call Communism a religion. At most, it’s a philosophical viewpoint. When I think of a religion, I think of three key aspects that are required (all three of them, or at least two):
1. A deity
2. Supernatural elements/creatures/abilities
3. An afterlife
Communism has none of those (or at most, it probably has supernatural elements if their researching PSI is of any indication). The Nazis could at least claim to religion under a pagan sense. Same goes for the Japanese with their Shinto Buddhism.
“the Japanese with their Shinto Buddhism.”
Shintoism and Buddhism are two very different religions.
Buddhism is from India, but Shintoism is native to Japan.
Shintoism was the State religion, which declared the Emperor to be the divine descendant of the Shinto Sun Goddess Amaterasu (the reason for the sun on the flag). Shintoism also proposed that all ethnic Japanese were racially connected to this divinity, but that no other races/ethnicities could be.
There is nothing like any of that in Buddhism, which is explicitly universal to all.