Complex sentence: The Kzinti call themselves "Heroes" or the "Heroes Race" and because they believe themselves to be "heroes", their society places a very high value on "acting Heroic" and behaving in a heroic fashion.
Split into simpler sentences: The Kzinti call themselves "Heroes" or the "Heroes Race" and because they believe themselves to be "heroes". Their society places a very high value on "acting Heroic" and behaving in a heroic fashion.