When the number of individuals within a group or population or species suddenly decline it is termed as population crash. This term is often referred when the human population declines suddenly impacting the economy and the quality of life.
The causes of population crash includes competition for the environmental resources required for survival is under scarcity and this implies only the fittest can survive according to the Darwin’s theory. The other major reason can be any natural disaster like floods, droughts, earthquake, volcanic eruption, fire, incidence of some disease or epidemic condition.