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 coalesce into kingdoms; by 1700 around eight kingdoms existed in 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.