Final answer:
The main focus of exploration/colonization in the 1400s was the Indigenous peoples of the Americas. Option d) is the correct answer.
Step-by-step explanation:
The main focus of exploration/colonization in the 1400s was: d) Indigenous peoples of the Americas.
During this time, European explorers mistakenly believed they had reached the East Indies and encountered the Indigenous peoples of the Americas. These early explorers called them Indians. The Indigenous population of the Western Hemisphere was estimated to be around seventy-five million, with over six hundred groups or tribes in North America alone.