When Hugh Harman made PEACE ON EARTH, he intended it to be an ambitious anti-war film. He later said he wanted to make it a longer 2-reel cartoon. Nonetheless it turned out to be one of the greatest and most chilling cartoons to come from Hollywood's animation golden age.
Despite being an anti-war film from the late 1930's, the message isn't very clear, beyond demonstrating man's inability to maintain a peaceful society with animals succeeding after man's demise. There are religious icons sprinkled throughout the film, but there aren't used to preach any messages, as one would suspect from a film of this kind. Their presence in the film also seem vague.
The elder squirrel's recollections of man's war echoes the horrors of World War I, which was still strongly in the public's recollection at the time. In fact, it almost feels like an alternative timeline of WWI.
Harman and Ising were known for trying to compete with Disney. They were really the only men that come close to replicating Disney's polished animation, but storytelling was not their strength. Nonetheless, this is one of Harman's best films. Unlike most Christmas films, this one can be unnerving to some audiences due to its grim war sequences and outcomes. A post-apocalyptic film before the genre even existed (without nuclear weapons obviously).
Remade by Hannah-Barbera in 1955 as GOOD WILL TO MEN with updated horrific war imagery reflecting the Cold War and a more clear cut religious message.