Answer:
The main reason would be the necessity for self-governing, as mother country usually did not valued the rights of colonists as they valued the rights of people in homeland.
Step-by-step explanation:
The best example for this are thirteen British colonies in America.
Colonists had to pay high taxes, they didn't have representatives in the British Parliament and generally were regarded as a citizens with less importance.
Therefore, when they started asking for more rights, Britain responded by imposing stricter laws. That is why at the end they realized that the only solution is to create independent state.