Colonization can be defined as some form of invasion, dispossession and subjugation of a people. It is is the action or process of subjugating another people or area by colonial policies  

The invasion need not be military; it can begin—or continue—as geographical intrusion in the form of agricultural, urban or industrial encroachments. The result of such incursion is the dispossession of vast amounts of lands from the original inhabitants. This is often legalized after the fact.

The long-term result of such massive dispossession is institutionalized inequality. The colonizer/colonized relationship is by nature an unequal one that benefits the colonizer at the expense of the colonized.

Colonialism is the practice of extending and maintaining a nation’s political and economic control over another people or area. 

Ongoing and legacy colonialism impact power relations in most of the world today. For example, white supremacy as a philosophy was developed largely to justify European colonial exploitation of the Global South (including enslaving African peoples, extracting resources from much of Asia and Latin America, and enshrining cultural norms of whiteness as desirable both in colonizing and colonizer nations).

See also: Decolonization