The setup is '7 Samurai'!!!
I've seen this movie before but this time it struck me:
The bandits will return at the end of the harvest (and when they do the town will starve) and one intrepid soul goes off on the unlikely mission to find warriors to defend the farmers (ants).
Of course the story diverges from there... but still I've gotta believe the Pixar people knew what they were referencing at the opening of the story.
"The good end happily, the bad unhappily, that is why it is called Fiction."