What are the causes for human migration and the refugee crisis in the modern era?

War and Famine raging in Syria, leaving hundreds of thousands of innocent people homeless.

As well as rising tides on island nations, most notably Micronesia and Malaysia. leaving them stranded and forced to seek higher ground

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

manchester's leaders hoped to oppress its working class to benefit factory owners.

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.