The Hausa Kingdoms, also known as Hausaland, were a collection of states started by the Hausa people, situated between the Niger River and Lake Chad in modern-day northern Nigeria. The Hausa people arrived in Hausaland during the first millennium CE as a result of the westward expansion of Hausa peoples. They started cultivating grains, which led to a denser peasant population. They had a common language, laws, and customs. The Hausa were known for fishing, hunting, agriculture, salt-mining, and blacksmithing. The Hausa Kingdoms were not a centralized empire but a loose confederation of city-states that often worked together but also competed with one another through trade. This vibrant trade helped them remain independent of the other large empires nearby for a thousand years before finally being conquered. The Hausa Kingdoms were conquered around 1808 by the rising Sokoto Caliphate. The seven true Hausa states, or Hausa Bakwai, were Biram, Daura, Gobir, Kano, Katsina, Rano, and Zaria (Zazzau), and their seven outlying satellites, or Banza Bakwai, were Zamfara, Kebbi, Yauri, Gwari, Nupe, Kororofa (Jukun), and Yoruba. Each city generally specialized in certain goods or economic activities. Rural Hausa populations were farmers who worked the land which belonged to the community as a whole. Over time, as the city-states became more centralized, this system was corrupted by the kings giving out parcels of land as rewards to certain individuals. Hausa agriculture also became heavily reliant on slaves.