The leaders of the school of Barbizon were: Georges Michel, Théodore Rousseau, Jean-François Millet and Corot. With them farmers no longer formed the elements of a decor but became true actors in their paintings. Millet devoted himself to farming scenes while Courbet showed a keen interest in workers, grave-diggers, woodmen or poachers. There was therefore a real description of the working class through many works
Casseurs de pierres, 1849
which glorified the hard work of farmers and their likes. Millet was not really an artist advocating some kind of revolution but originally a farmer attracted by the land which he wanted to depict so as to demonstrate that one could think deeply about the people who were living in the countryside. Courbet, who was rather more a Marxist before Marxism even existed, was fighting for more social justice.
Most of the painters of the school of Barbizon were rejected from the major Paris Salons of their time and exuded some kind of revolt against the industrial society in their works. Rousseau, Daubigny tried to show the true countryside in their paintings while polluting cities were mushrooming not far away, while rivers became scarce and while forests were cut by new roads.
In that sense they proved to be true ecologists trying to find some fresh air and open panoramas far from the urban chaos.