What does Doctor Dolittle blame for causing the war between the Bag-jagderags and the Popsipetels in the novel, The Voyages of Doctor Dolittle?

After the war Dolittle lambastes the Bag-jagderags for what he feels caused the war: laziness. The Bag-jagderags were too lazy to till the land themselves, so they attack the Popsipetels to rob them of their corn.