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

HUman migrations is the cause of unemplyment and war, in the modern ear. Devloping nations like India, Pakistan etc. have a huge population, which is not able to find job in their himeland and thus migate to other nations.
Middle aestern nations like Syria, Iraq, Libya, Sudan etc. are suffering from war and terrorism, which is forcing them to inhabit a peaceful and livable area. 

The middle ages were dominated by Christianity. So the number would be expected to be high.