Gaullist foundation of the Fifth Republic. Without such a threat, there were no longer grounds for a tacit alliance or ' Popular Front' of understanding between conservative -- or centrist -- liberals and Marxists.
At one time, conservative liberals were seriously constrained by the anti-liberal political forces on their right. Left-liberals were at the same time conscious of a betrayal of the 'social' promise of Republicanism by governing conservatives, while the socialist left went so far as to call into question the very nature of the Republic, as a bourgeois class state. Given the necessity of making common cause against the right, both at home and abroad, these differences tended to foster a leftward drift in the 'official' interpretation of the Revolution. The political center was largely obliged to keep still -- or risk open identification with the right -- while the social interpretation grew steadily more emphatic in its class analysis. In the end, the conservatives were confronted with an outspoken Marxist in the Sorbonne.
Yet with real changes in the political realities, the tide of ideas began to turn. The development of profoundly conservative liberal sociological theories in the United States, to counter the more critical traditions of social theory, began to influence French social history in ways which were not at first obvious. Emmanuel Le Roy Ladurie, for one, went in search of Marx, but found Malthus. When, at the same time, the official historiography of the Revolution was becoming ever more explicitly grounded in Marxist theory, and both Montagnard politics and the revolutionary popular movement were being sympathetically evoked by Rudé and Soboul, the appearance of a conservative, revisionist interpretation of the Revolution should not be surprising.