In the Republic Plato argues for a purely materialist and internal explanation for war: states attack their neighbors to gain their possessions, especially their land. He can imagine a city fighting such a war to escape poverty: the people in the Republic's original, self-sufficient city will not have too many children “lest they fall into either poverty or war.” But the main thrust of his argument is that the “unlimited acquisition of wealth, disregarding the limit set by our necessary wants” drives cities to war.” In the Phaedo Plato specifies the reason why people want “wealth and luxuries” and sums up the entire causal chain:

Plato thus attributes the drive to war to the desires of the body and links it with a deplorable lack of individual self-restraint. These attitudes find parallels among critics of Athenian foreign policy such as Isocrates.

Aristotle does not provide an overarching theory of the cause of war, but he too mentions material motivations for war.