European countries colonized other lands in the 1500s due to declining natural resources and overpopulation at home. By colonizing the Americas, European colonists gained access to new lands and opportunities but killed, enslaved, or displaced millions of native Americans in the process. The European colonization of the Americas resulted in genocide of native peoples and was one of the bloodiest periods in human history. European colonists also brought African slaves to the Americas to work, especially after native Americans proved to not survive slavery well. Colonialism essentially involved foreign groups invading, killing, enslaving, or displacing indigenous populations and establishing control over new territories and peoples.