- Open Directory Science: Social Sciences: Political Science: Political Philosophy: Political Philosophers: Engels, Friedrich
- Open Directory Science: Social Sciences: Economics: Schools of Thought: Marxian
- Open Directory Society: History: By Topic: Social History: Revolutions and Social Movements: 1848 Revolutions
- Open Directory Society: Politics: Socialism: Marxism
- Open Directory Society: Philosophy: Philosophers: H: Hegel, Georg Wilhelm Friedrich