Final answer:
Bartolomé de Las Casas helped popularize the Black Legend of Spain, which claimed that the Spanish were cruel conquerors. This notion was used by Spain's rivals, like the English, to justify their own colonization projects.
Step-by-step explanation:
Bartolomé de Las Casas helped popularize the so-called "Black Legend" of Spain, which indicted the empire for its horrific treatment of Native people. The Black Legend refers to the idea that the Spanish were bloodthirsty conquerors with no regard for human life. This notion was used by Spain's imperial rivals, particularly the English, to justify their own colonization projects and demonize the Spanish. However, it is important to note that all European colonizers, including the English, shared a disregard for Native peoples.