In part due to Cuban slaves working primarily in urbanized settings, by the 19th century, the practice of had developed (or "buying oneself out of slavery", a "uniquely Cuban development"), according to historian Herbert S. Klein. Due to a shortage of white labor, blacks dominated urban industries "to such an extent that when whites in large numbers came to Cuba in the middle of the nineteenth century, they were unable to displace Negro workers." A system of diversified agriculture, with small farms and fewer slaves, served to supply the cities with produce and other goods.