American economist Malthus proposed: The trend of population growth is always faster than the growth of production  If it is not controlled, the population will always grow in a geometric progression, while the means of subsistence can only grow in arithmetic progression
When the population expands to the limit where the means of subsistence can only survive, hunger, war and disease will appear
The incoordination between the rate of population growth and the rate of production growth will lead to follow-up problems such as wars.