Colonialism is when a group of people from one country invade and take control of another country. They come in with their own government, and they decide how the people of the other country should live, what laws they should follow, and sometimes they even take away the people's land, resources and rights. This can happen when one group is powerful, and doesn't respect the rights of the people living in the other country. It can be very unfair and hurtful for the people in the other country.