Changes in society that cause large numbers of people to move up or down the class ladder, which causes one class to increase while others decrease, is called mobility.

This is called social mobility. Social mobility can happen to an individual, a family, a locality even up to a whole nation. This change is usually observed in the change of wealth, leading an entity to be considered in another class different from their original or previous class. 

Fixing the errors and resubmitting it