Describe two socioeconomic factors that contributed to the spread of the bubonic plague (the black death) throughout china and western europe.

The bubonic plague was spread by fleas on the backs of rats, rats propagate in urban areas and in areas with great amounts of filth. At the time, the urban population was at an all time high in Europe, and the strain of pushing more and more people into already densely populated areas was really unsanitary conditions. Sewage would often be thrown directly into the street and refuse was often left for months or years accumulating before it became enough of a problem where it'd have to be cleaned up, this was rat heaven. Also with most people migrating into urban areas coming in dirt poor and looking for a job,  many were living in houses with dozens of other people and in close quarters disease spreads easily, and there were tons of poor people living in these cities at this time. Eventually once the plague killed enough people, bodies lined the streets everywhere and the plague slowly worked it's way through populations, the rats feeding and thriving on the dead created by the disease, growing in numbers and spreading as the disease did.