Colonialism
There are several different types of colonialism.  Some countries that expanded their territory made settler colonies.  Some countries that started out as settler colonies include the United States, Canada, Australia, New Zealand and the states of Latin America.  In all of these countries, people from European countries moved to the best parts of the new place, and forced the indigenous peoples (such as Indians, Maori, etc.) to move. When the local people or tribes had to move, it caused a lot of problems. Many of these indigenous peoples were also enslaved, killed through genocide or died in pandemics because they had no immunity against infectious diseases brought by the settlers.