Lefebvre began writing in 1904, but it was not until 1924, at the age of fifty, that he was finally at the point in his career - no longer preoccupied with supporting his family - that he was able to finish his doctoral thesis: "Les Paysans du Nord pendant la Révolution française". This work was a detailed and thorough examination of the effects of the French Revolution on the countryside. Lefebvre’s work on this thesis was "based on a thorough analysis of thousands of tax rolls, notarial records, and the registers of rural municipalities, whose materials he used to trace the effects of the abolition of feudalism and ecclesiastical tithes, the consequences of property transfers, the movement of the bourgeoisie onto the countryside, and the destruction of collective rights in the peasants villages".