Colonialism, the process of a country taking control of a territory outside of the defined borders of its nation-state, has been driven primarily by a desire for wealth and to maximize profit. It started with the Spanish in the New World, who sought gold on the newly-discovered American continents and then realized the vast money that could be earned by systematically exporting the natural resources and establishing an agricultural base. They had a larger population, a superior military capability, and different ideas about ownership than Native Americans, and they were quick to exploit their own advantages.
Other European countries wanted to start colonies as well once they realized the kind of wealth that was flowing into Spain. Nations such as Great Britain realized there was much greater potential to harness and manage resources if they could manage to establish colonies and set up political administrations and infrastructure on the new continent. Britain sponsored colonies, which, in the end, paid off quite handsomely.
European nations also used the colonies as a dumping ground for undesirable elements, shipping out—or allowing to leave—religious dissidents and criminals.