Προέλευση μαχητών του ISIS....

Feed - Quora

They come from all over the world.

I would highly recommend to read Soufan Group Report on that matter:

BEYOND THE CALIPHATE: Foreign fighters and the Threat of Returnees [PDF]

Based on that report, here the main countries:

As you can see leading countries are: Russia, Saudi Arabia, Jordan, Tunisia and France.

But ISIS countries are coming from many regions:

I was really surprised to discover, that ex-USSR suppressed Middle East (except Iraq and Syria) in the number of foreign fighters.

Here is map I made based on this report. Now, I should warn you that this map is not completely accurate because data for some countries are from 2016 and for others from 2017, but this map show general picture of what is happening.

Countries mapped:

white - no date or none

grey - Iraq and Syria

green - < 50

yellow - 50 - 100

brown - 101 - 500

purple - 501–1000

red - more than 1000

Countries that are not visible:

Trinidad and Tobago - 138 fighters

P.S. Just click on the map, it will get bigger