Europeans justified colonizing North America for several key reasons:
1) Prejudice - Europeans viewed themselves as superior and did not understand indigenous groups who resisted change to their lands and way of life.
2) Slavery - The slave trade brought thousands of Africans to the Americas to work plantations, and many Europeans believed slavery was acceptable. They engaged in the triangular slave trade between West Africa, the Caribbean/American colonies, and Europe.
3) Economic benefits - Colonies were expected to provide resources to enrich European empires through controlled trade like the Navigation Acts. Britain particularly benefited economically from the slave trade and goods produced in the colonies.