Nigeria's top contribution to Africa's agenda of decolonisation and anti-racism was mostly enhanced with the formation of the_________

The correct answer is the Organization of African Unity (OAU), which was formed in 1963. The OAU was established with the goal of promoting unity and cooperation among African countries, particularly in the face of colonialism and racism. The organization aimed to promote decolonization and anti-racism initiatives on the continent, and to work towards the liberation of African countries still under colonial rule. It played a significant role in the struggle against apartheid in South Africa, and helped to bring an end to colonialism in many other African countries. The OAU also served as a platform for African leaders to discuss and address issues facing the continent, such as conflict, economic development, and political stability.