A defining feature of Greek society was the distinction between those who could afford to live off the labour of others, 'the rich' or leisured classes, and those who had to earn a livelihood, 'the poor' or working classes. A second defining feature of Greek society was pervasive competitiveness. Competition for wealth within a community aggravated the pressure on resources created by the leisure-class aspirations of its citizens. Aristotle noted that 'people commit the greatest acts of injustice for the sake of superiority, not for the sake of necessity': the root of conflict was pleonexia. Aristotle briefly argued in his Politics that the growth of hoplite forces had led to wider political participation, and added that it was in particular the small size of the 'middle group' which had previously allowed oligarchic regimes to flourish. Wars were common, and links between social and political structures on the one hand, and military institutions on the other, were close.