Final answer:
Bartolomé de las Casas was chosen by the Spanish Crown to assess the treatment of Native Americans due to his transition from encomendero to a passionate defender of Native American rights, his impactful advocacy leading to the New Laws of 1542, and his authority on the matter recognized by the Crown.
Step-by-step explanation:
Bartolomé de las Casas was chosen by the Spanish Crown to assess the treatment of Native Americans because he had become a fervent advocate for their rights. Initially coming to the New World as an adventurer and encomendero, de Las Casas underwent a profound change of heart in 1514. After witnessing the brutal treatment of Native Americans under the encomienda system, he renounced his own encomienda and began to vigorously advocate for the humane treatment of native peoples. His efforts were instrumental in influencing the issuance of the New Laws of 1542 by King Charles V of Spain, which sought to end the encomienda system and improve the treatment of the indigenous population.
Through his graphic descriptions of Spanish abuses in his work A Short Account of the Destruction of the Indies, de las Casas was able to communicate the severity of the situation to a wider audience, spurring reform. While initially being part of the problem, de las Casas dedicated the rest of his life to the cause of the natives, earning him a position of trust and authority with the Spanish Crown as an assessor of colonial practices.