Final answer:
Bartolomé de Las Casas wrote about the severe mistreatment of Native Americans by the Spanish, leading to the New Laws of 1542 that aimed to protect the indigenous peoples and end the encomienda system.
Step-by-step explanation:
The calamity Bartolomé de Las Casas referred to in his writings was the brutal mistreatment and exploitation of Native Americans by the Spanish colonizers. Las Casas, who was initially part of the colonial system as an encomendero, experienced a profound change of heart in 1514 and became an advocate for the rights and fair treatment of the indigenous peoples. His most influential work was A Short Account of the Destruction of the Indies, where he vividly described the atrocities committed by the Spanish against Native Americans, labeling them as merciless and inhumane. Las Casas's efforts ultimately contributed to the establishment of the New Laws of 1542, which were intended to improve the treatment of the Native Americans and to dismantle the encomienda system, despite strong opposition from Spanish settlers in the Americas.