Theorien über den Mehrwert
Sismondi's theory of periodic crises was developed into a theory of alternating "cycles" by Charles Dunoyer, and similar theories, showing signs of influence by Sismondi, were developed by Johann Karl Rodbertus. Periodic crises in capitalism formed the basis of the theory of Karl Marx, who further claimed that these crises were increasing in severity and, on the basis of which, he predicted a communist revolution. Though only passing references in "Das Kapital" (1867) refer to crises, they were extensively discussed in Marx's posthumously published books, particularly in "Theories of Surplus Value". In "Progress and Poverty" (1879), Henry George focused on land's role in crises – particularly land speculation – and proposed a single tax on land as a solution.