What is the theme in The Pushcart War by Jean Merrill?

There are several points within the narration of this novel that a reader might see resemblance to the Revolutionary War. For example, the Tacks Tax seems to closely resemble the tea tax levied on American colonists by the English king. There are also other points in which the reader might see reference to the biblical battle between David and Goliath, such as the peace march where General Anna and her troops face down a Mighty Mammoth with nothing more than their pushcarts. These bits of resemblance have one thing in common, the battle of a large adversary, or giant, against a smaller opponent. A reader will be hard pressed to imagine a more outsized opponent than a pushcart.