Which of the following terms refers to people who worked in Northern factories under harsh conditions?

The term that best refers to people who worked in Northern factories under harsh conditions is "wage slaves." This term emerged in the 19th century to describe the plight of factory workers who, despite being paid wages, faced extremely difficult working conditions, long hours, and low pay. The term highlights the economic dependency of these workers on their jobs, which often left them in precarious situations, similar to those in servitude. Many factory workers lived in poverty and had minimal rights, leading to the notion that they were "enslaved" by their economic circumstances, despite technically being free.

The other terms mentioned do not accurately capture the situation of Northern factory workers. Yeomen farmers, for instance, were small-scale farmers in the South who owned their land and worked it themselves, far removed from the industrial workforce of the North. Urban laborers is a broader term that could apply to any workers in cities, not specifically emphasizing the harsh conditions of factory life. Indentured laborers were individuals who signed contracts to work for a fixed number of years in exchange for passage to America or other benefits, distinctly different from the conditions faced by Northern factory workers.