Final answer:
The term 'second middle passage' is used by historians to describe the domestic slave trade within the United States, echoing the disruptive and horrific journey of the original Middle Passage of the Atlantic slave trade.
Step-by-step explanation:
Historians refer to the slave trade within the United States as the second middle passage because it represents an internal forced migration similar to the infamous Middle Passage across the Atlantic. These domestic movements occurred between 1820 and 1860, where White American traders sold a million or more captives, transported by ship or overland, from older states like Virginia to newly developing areas like Alabama. This domestic slave trade was an economic cornerstone in the antebellum South, with a significant impact on the economy and the lives of enslaved people that paralleled the horrors of the original Middle Passage.