France's imposition of a head tax in 1900, aimed at enabling the colony to undertake a public works program, provoked a number of revolts. The public works programs undertaken by the Ivorian colonial government and the exploitation of natural resources required massive commitments of labor. The French therefore imposed a system of forced labor under which each male adult Ivorian was required to work for ten days each year without compensation as part of his obligation to the state. The system was subject to extreme misuse and was the most hated aspect of French colonial rule. Because the population of Ivory Coast was insufficient to meet the labor demand on French held plantations and forests, which were among the greatest users of labor in French West Africa, the French recruited large numbers of workers from Upper Volta to work in Ivory Coast. This source of labor was so important to the economic life of Ivory Coast that in 1932 the AOF annexed a large part of Upper Volta to Ivory Coast and administered it as a single colony. Many Ivorians viewed the tax as a violation of the terms of the protectorate treaties because it seemed that France was now demanding the equivalent of a "coutume" from the local kings rather than the reverse. Much of the population, especially in the interior, also considered the tax a humiliating symbol of submission.