The concept of colonialism refers to the process by which

A authority exerts a control over a territory occupied by itself, generally using military power or a representative of government in a country or territory to which did not belong to it.

Detailed explanation:

Colonialism is a form of imposing authority from one culture over another. It can happen in a forced way, with the use of military power or by other means such as language and art. Portuguese domination in Brazil is a good example of colonialism, as well as the colonization of Africa, by the destruction of the culture of the Andean peoples and the influence of European culture in underdeveloped countries.