The power of traditional chiefs was gradually eroded by:

British colonial policies
Spread of Christianity
Modern education
All of the above

The correct answer is: All of the above.

British colonial policies, the spread of Christianity, and modern education all contributed to the erosion of the power of traditional chiefs.

British colonial policies often undermined the authority of traditional chiefs by appointing their own officials to administer the colonies. This led to a loss of respect for traditional chiefs and a decline in their power.

The spread of Christianity also contributed to the erosion of the power of traditional chiefs. Christianity taught people that they were equal in the eyes of God, which undermined the traditional hierarchy in which chiefs were at the top.

Modern education also contributed to the erosion of the power of traditional chiefs. Modern education taught people about new ideas and ways of life, which made them less likely to follow the traditional customs and practices of their chiefs.

In conclusion, British colonial policies, the spread of Christianity, and modern education all contributed to the erosion of the power of traditional chiefs.