Concept:Agricultural surplus from improved farming made it possible for large, organised societies to develop.
Explanation:Early communities in Nigeria first depended on hunting and gathering, which could only support small groups.
The gradual development of agriculture allowed people to settle permanently in one place.
Improved farming methods produced surplus food beyond what families needed for daily survival.
This surplus supported a growing population and freed some individuals from constant food production.
Those individuals became rulers, priests, traders, and craft specialists, leading to the specialisation of labour.
Economic growth and organised leadership encouraged the emergence of centralised authority and political states.
These developments took place long before European contact, so colonization is not the cause.
The Industrial Revolution is also a later event and is not connected to the formation of early Nigerian states.
Agriculture thus remains the most significant factor behind the rise of early states in Nigeria.
Answer:D. Agricultural advancements