What are some causes and effects of rapid population growth between 1900 and 1945?

from the conditions of the working class in england by friedrich engels,the main idea is :

no options provided, here,but the answer to this question is often: a historian cites a japanese newspaper article published a year after the end of world war ii in order to draw conclusions about the effect of the war on the japanese economy.

clearly from the answer, the historian alludes to historical sources,and records to aid in analyzing and drawing conclusion on the effect of the war on the economy of japan.