How did the Tang & Song Dynasties maintain and justify their rule?

Through the principle of Mandate of Heaven.

Explanation:

Mandate of Heaven refers to the belief that whoever become the rulers in China obtain the position because the Gods intended them to. So, they believe that  if one ruler is killed and changed by another rulers, it happened because the initial ruler is deemed as 'unworthy' by the heaven to continue his reign.

Many people in Tang & song dynasties justify the cruel things that they did through this belief. The see that the word of the emperor is the word from the heaven that must be obeyed by all citizens.

the mother countries succeed in doing that by using the colony's natural resources, facilities in a colony, they do not take good care of these facilities, causing them to fail. this has had negative and positive effects on the people of africa, they then governed through direct or indirect rule depending on the country.

hope thsi