The Berlin Conference of 1884 assigned the territory to Germany as part of German East Africa, marking the beginning of the colonial era. The explorer Gustav Adolf von Götzen was the first European to significantly explore the country in 1894; he crossed from the south-east to Lake Kivu and met the king. The Germans did not significantly alter the social structure of the country, but exerted influence by supporting the king and the existing hierarchy and delegating power to local chiefs. Belgian forces took control of Rwanda and Burundi in 1916, during World War I, beginning a period of more direct colonial rule. Belgium ruled both Rwanda and Burundi as a League of Nations mandate called Ruanda-Urundi. The Belgians also simplified and centralised the power structure, and introduced large-scale projects in education, health, public works, and agricultural supervision, including new crops and improved agricultural techniques to try to reduce the incidence of famine. Both the Germans and the Belgians promoted Tutsi supremacy, considering the Hutu and Tutsi different races. In 1935, Belgium introduced identity cards labelling each individual as either Tutsi, Hutu, Twa or Naturalised. While it had previously been possible for particularly wealthy Hutu to become honorary Tutsi, the identity cards prevented any further movement between the classes.