Pure propaganda.

A message about how German soldiers in WWII followed orders without question and destroyed the people the conquered. A message about how common folk can resist these conquerors, how an invasion is not defeat as long as you struggle against oppression, and how you can never truly conqueror a country that resists you. It's a blatant over the top message, but it's still Steinbeck.

The characters are wonderful, fully realized, and unique. The imagery brings the setting to life. Good and bad, characters face moral dilemmas.

The language is Steinbeck even if he beats you over the head with his message.

A wonderful short read.