Foucault's work from Society Must be Defended onwards needs to be understood in relation to Montesquieu and Tocqueville. We could even read Foucault as the third figure in a French liberal triumvirate spanning three centuries. This reading may have some problems attached to it, but no more than the other readings of Foucault around and less than most. Foucault's reputation has been taken over by Post-Marxist/ Post-Modernist/Post-Structuralist leftists for whom liberalism is a dirty word. However, Society Must be Defended coincides with a liberal revival in France which includes a Tocqueville revival. It uses the terms and references of the two great French liberals (and republicans). It's concerned with the kind of liberty that can exist under different kinds of regime. It's concerned with the limitation of society in relation to the state. It uses Montesquieu to establish the evolution of the French state, bureaucracy and aristocracy in the Eighteenth Century. The understanding of the relation between the Ancien Regime and the French Revolution follows the analysis of Tocquville's book of that name. Foucault refers to majoritarian and demagogic aspects of the emergence of left wing and democratic politics, very much in line with Tocqueville's understanding of the possible dangers of democracy.
The reading of Foucault's later work will be very incomplete until it is thoroughly understood and discussed in the terms of his two French predecessors in social and political thought devoted to liberty.