European countries colonized other lands in the 1500s due to dwindling natural resources and pollution at home. As they colonized the Americas, millions of Native Americans were killed, enslaved, or forced from their lands, making it a horrific period in history. European colonists also brought African slaves to the Americas to work, especially after Native Americans proved to die in slavery. Colonialism involved invading communities, killing or enslaving the inhabitants, and taking over their lands and resources through violence and warfare.