Sugar is different from honey. It offers a stronger sweet flavor, and like steel or plastic, it had to be invented. In the Age of Sugar, Europeans bought a product made thousands of miles away that was less expensive than the honey from down the road. That was possible only because sugar set people in motion all across the world—millions of them as slaves, in chains; a few in search of their fortunes. A perfect taste made possible by the most brutal labor: That is the dark story of sugar.
–Sugar Changed the World,
Marc Aronson and Marina Budhos
What is the authors’ claim in this passage?

What is the authors’ primary purpose in the passage?