rather than a racial one. The earliest form of social organisation in the area was the clan (ubwoko). The clans were not limited to genealogical lineages or geographical area, and most included Hutu, Tutsi, and Twa. From the 15th century, the clans began to merge into kingdoms. One kingdom, under King Gihanga, managed to incorporate several of its close neighbor territories establishing the Kingdom of Rwanda. By 1700, around eight kingdoms had existed in the present-day Rwanda. One of these, the Kingdom of Rwanda ruled by the Tutsi Nyiginya clan, became increasingly dominant from the mid-eighteenth century. The kingdom reached its greatest extent during the nineteenth century under the reign of King Kigeli Rwabugiri. Rwabugiri conquered several smaller states, expanded the kingdom west and north, and initiated administrative reforms; these included , in which Tutsi patrons ceded cattle, and therefore privileged status, to Hutu or Tutsi clients in exchange for economic and personal service, and , a corvée system in which Hutu were forced to work for Tutsi chiefs. Rwabugiri's changes caused a rift to grow between the Hutu and Tutsi populations. The Twa were better off than in pre-Kingdom days, with some becoming dancers in the royal court, but their numbers continued to decline. The Berlin Conference of 1884 assigned the territory to the German Empire, who declared it as part of the German East Africa. In 1894, explorer Gustav Adolf von Götzen was the first European to cross the entire territory of Rwanda, he crossed from the south-east to Lake Kivu and met the king. In 1897, Germany established a presence in Rwanda with the formation of an alliance with the king, beginning the colonial era. 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 invaded Rwanda and Burundi in 1916, during World War I, and later, in 1922, they started to rule both Rwanda and Burundi as a League of Nations mandate called Ruanda-Urundi and started a period of more direct colonial rule The Belgians simplified and centralised the power structure, 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, in the wake of New Imperialism, promoted Tutsi supremacy, considering the Hutu