When a powerful country conquers a territory, it becomes its colony. The colonizer than has control over it and everything in it, including its riches. It takes advantage of the colony's natural riches, as well as the taxes that the people have to pay to the mother country. So obviously the colonizer wouldn't want to support colonial independence because that would mean terrible loses for its own bank. Additionally, other countries wouldn't want to support it either because it would mean war against the initial colonizer in such a case.
