The most significant factor which accounts for the rapid growth in the population of the capital cities of West Africa is

The most significant factor accounting for the rapid growth in the population of the capital cities of West Africa is "rural-urban migration". This refers to the movement of people from rural areas to urban areas, such as cities, in search of better economic opportunities, education, healthcare, and other amenities. In many West African countries, the rural areas are characterized by poverty, lack of infrastructure, and limited access to essential services. As a result, many people are forced to move to urban areas, including the capital cities, to seek better opportunities and living conditions. The rapid growth in the population of these cities has put a strain on the available resources and infrastructure, leading to overcrowding, traffic congestion, and other social and environmental problems. Therefore, policies and interventions that address the root causes of rural-urban migration, such as rural development, job creation, and access to basic services, are necessary to mitigate the negative impacts of urbanization and promote sustainable development.