 During the 1920s and 1930s the French introduced a policy of mandatory cotton cultivation, a network of roads was built, attempts were made to combat sleeping sickness, and Protestant missions were established to spread Christianity.New forms of forced labor were also introduced and a large number of Ubangians were sent to work on the Congo-Ocean Railway.Through the period of construction until 1934 there was a continual heavy cost in human lives, with total deaths among all workers along the railway estimated in excess of 17,000 of the construction workers, from a combination of both industrial accidents and diseases including malaria.