Five hundred years before Christ, there arose in central Nigeria a culture that was among the most advanced and richest of the ancient world. By the first millennium, Islam had come to Nigeria and three centuries later, trade routes emanating from northern Nigeria stretched from Africa to Europe and the Middle East. Portugal was the first European power to establish trading stations in the 1400s. The Dutch, British, and other countries vied with Portugal to control the lucrative slave trade that was organized out of Nigeria and by the 1700s, the British controlled most of the coastal region. The tide changed after Britain abolished slavery and sought to eliminate slave trading. In 1861, Nigeria was made a British colony and in 1906, land east of the Niger River was incorporated into the colony. Slowly, Britain began to prepare the country for self-rule: in 1946 Britain divided Nigeria into three parts, each with an advisory assembly. Nigeria was restructured as the Nigerian Federation in 1954. The country experienced difficulties in the 1960s as the various ethnic groups making up the country battled for control. In 1966, a civil war erupted following a coup in which the prime minster and many others were killed. Between 1967 and 1970, the war in Biafra raged. Biafra was the region that seceded from Nigeria after rejecting a plan that divided the country into 12 states. This devastating conflict cost the lives of at least a million Biafrans (mostly of the Ibo tribe) and severely damaged the Nigerian economy. But through the years, political instability, as manifested by coup after coup, has been a constant in the country. In 1999, the first popularly-elected president in 16 years came into office.In 1999, a new constitution was adopted and a peaceful transition to civilian government was completed. The government continues to face the daunting task of institutionalizing democracy and reforming a petroleum-based economy, whose revenues have been squandered through decades of corruption and mismanagement. In addition, Nigeria continues to experience longstanding ethnic and religious tensions. Although both the 2003 and 2007 presidential elections were marred by significant irregularities and violence, Nigeria is currently experiencing its longest period of civilian rule since independence. The general elections of 2007 marked the first civilian-to-civilian transfer of power in the country's history. National and state elections in 2011 and 2015 were generally regarded as credible. The 2015 election was also heralded for the fact that the then-umbrella opposition party, the All Progressives Congress, defeated the long-ruling People's Democratic Party that had governed since 1999, and assumed the presidency, marking the first peaceful transfer of power from one party to another. Presidential and legislative elections were held in early 2019 and deemed broadly free and fair despite voting irregularities, intimidation, and violence.