Push
In western Europe there is three major push factors, little to no job opportunities, migration of foreign people, and change of landscape. Lets go economically first. There is a few jobs to offer in western Europe because of the economic restructuring going on. Next is Immigrants, they are pouring all over western Europe and some people don't like that so they leave. Lastly landscape, its changing over west Europe because of floods and because of immigrants coming in cities and since some don't have space, they create places were they could live which changes the landscape.
Pull
People/Immigrants move to west Europe for many reasons. One reason is for safety. Some people that used to live in their home countries might have moved because of war. Since Europe is not as bad as it used to be in 1918 and 1944 more people tend move to this region. Last reason is because of Europe's abundance of resources, other countries in the middle east or in Africa might not have as much natural resources as this region.