The next thirty years were marked by mostly small scale revolts against French rule and the development of a plantation-style economy. From 1920 to 1930, a network of roads was built, cash crops were promoted and mobile health services were formed to combat sleeping sickness. Protestant missions were established in different parts of the country. New forms of forced labor were also introduced, however, as the French conscripted large numbers of Ubangians to work on the Congo-Ocean Railway; many of these recruits died of exhaustion and illness as a result of the poor conditions.