Manchester's growth is closely linked with the cotton industry which relied heavily on colonialism and slavery as well as exploitation of the workers (men, women and children) by the mill owners. In 1851 the population was 303,382, during the next forty years it rose to over half a million by 1891 (563,368) although the American Civil War in the early 1860s caused a Lancashire Cotton Famine. Manchester's population, at the peak of the cotton industry in 1921, stood at 730,307. The industry declined after World War II and now many of the old mills and warehouses in the area are used for a variety of other purposes.
There's a website which gives details of old occupations. One of these is "Manchester warehouseman" which is the name given to someone who worked in a cotton warehouse during the period when Manchester was the centre of the cotton industry.