Final answer:
Christopher Columbus was the explorer who helped establish overseas empires and decimate indigenous populations for European powers, specifically under the Spanish flag, while Pedro Cabral was the first to claim Brazil for Portugal.
Step-by-step explanation:
The explorer who aided in establishing overseas empires for Portugal, Spain, England, and France and played a role in decimating indigenous populations was Christopher Columbus. Columbus's voyages under the Spanish flag led to the colonial expansion into the Americas. This expansion often involved the subjugation and devastation of indigenous peoples. The first explorer to reach Brazil and claim it for the throne of Portugal, however, was Pedro Cabral. Portuguese and Spanish colonization efforts were some of the earliest, with Spain credited with establishing the first colonies in the Americas soon after Columbus's initial voyage in 1492. The Spanish conquests included defeating indigenous empires like the Aztecs and the Inca and replacing them with colonial governments.
The explorer who aided in establishing overseas empires and decimating indigenous populations for Portugal, Spain, England, and France was Christopher Columbus (option d). Columbus, sponsored by Spanish monarchs, embarked on a voyage in 1492 and reached the Caribbean instead of Asia, initiating the era of Atlantic exploration. Following Columbus, other explorers like Hernán Cortés and Francisco Pizarro conquered the Aztec and Inca empires respectively, expanding the Spanish empire.