Where did the government of early African empires have in common?

Ancient Ghana ruled from around 300 to 1100 CE. The empire first formed when a number of tribes of the Soninke peoples were united under their first king, Dinga Cisse. The government of the empire was a feudal government with local kings who paid tribute to the high king, but ruled their lands as they saw fit.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.