Located in West Africa, Nigeria is the most populous country on the continent, with approximately 175 million inhabitants from more than 250 ethnic groups. The population is geographically split along ethnic and religious lines with a Muslim majority in the North and a Christian majority in the South. The earliest known civilization in the country was the Nok culture (800 BCE - 200 CE). During the middle ages, several independent city-states were established, some of which became important players in the slave trade. The Nigerian kingdoms remained independent until the late 19th century, when Britain began a colonizing campaign. The modern country of Nigeria gained independence in 1960, but a series of military coups took place during the next 40 years, stifling democracy and in some cases causing ethnic and religious conflict. The first open elections were held in 2003, though the country still has issues with ethnic and religious conflict.