Final answer:
Bartolomé de Las Casas' most influential writing was "A Short Account of the Destruction of the Indies" (1542), where he highlighted the mistreatment of Native Americans by Spanish colonists and inspired reforms.
Step-by-step explanation:
Bartolomé de Las Casas' most influential writing was the "A Short Account of the Destruction of the Indies" (1542). In this book, Las Casas detailed the mistreatment and exploitation of Native Americans by Spanish colonists. His writings had a significant impact on raising awareness of the brutal treatment of indigenous peoples and helped inspire the idea of the Black Legend. Las Casas' work ultimately led to reforms aimed at ending the encomienda system in the Spanish colonies.