All societies have ways of exercising authority, making decisions, and settling disputes. In the 1940s, anthropologists distinguished between those societies with informal means of accomplishing these functions and those with formal roles and systems for doing so. In acephalous societies such as bands and lineage orders, leadership is situational and temporary, and people make decisions using discussion and consensus. Leaders in such societies have persuasive power but no formal means of enforcing their will. In centralized societies such as chiefdoms and states, various forms of power are condensed in the formal hereditary role of the leader. As military leaders, chiefs and kings have coercive power to collect taxes and tribute, enforce their commands, settle conflicts, and wage war to enlarge their territories. As societies become more centralized, they also become more stratified, with social groups ranked according to wealth and power. With social stratification and centralized rule, systems of ideology and hegemony develop to support the social order. Modern nation-states combine the state apparatus with a strategically cultivated sense of peoplehood based on common culture. European colonialism imposed an authoritarian state form to rule over local forms of political organization such as chiefdoms and lineage orders, often malforming those original political forms. The structural and social problems of many postcolonial states are rooted in the destructive processes of colonialism. Outside of the formal realm of government, people seek to influence social and political conditions through social movements. Some social movements provide a means of expressing dissatisfaction, while others press for specific forms of social change or complete reorganization of the political order.