The Aro age-grade system in Igbo land was a political organization. The Aro were a powerful group in the eastern part of Nigeria, and their age-grade system was used to govern their society. The Aro age-grade system was made up of groups of people who were born in the same year, and each group was responsible for specific duties in the community. They were involved in everything from settling disputes to collecting taxes. The Aro also played a key role in the trans-Atlantic slave trade, acting as middlemen between European slave traders and African slaves.