Read the passage from Sugar Changed the World. In every single American slave state, the population of enslaved people kept rising even after the slave trade was abolished. That was because enough enslaved children were born, lived, and grew to become adults. There was just one exception to this rule: Louisiana, where the native-born enslaved population kept dropping. Sugar was a killer.

Unlike the Caribbean, Louisiana has cold snaps. That put an additional pressure on the sugar harvest. Not only did the slaves need to harvest the cane in perfect rhythm with the grinding mills, but the entire crop had to be cut down between mid-October and December. This pace only increased when growers installed improved, steam-powered mills. People needed to work faster than the weather and to keep pace with machines.

What is the authors’ purpose in this passage?