Why did they refer to the africans as robust?

They refered to the Africans as robust because before they enslaved Africans, they tried to enslave Native Americans; but things did not work out very well. The Native Americans were not very strong and neither were their immune systems. They got sick very often from the foreignors and died in great numbers. Afterwhich the Europeans looked for other people, more reliable people. They looked to Africa, and saw how the people were strong, healthy, hearty, and vigorous (robust).