According to a study from the Brookings Institution, which surveyed Twitter, Saudi Arabia, Syria, Iraq, the United States, and Egypt are the top locations where ISIS supporters claim as their location.
Perhaps unsurprisingly, nine of the top 11 countries where ISIS-supporters claimed to live were Middle Eastern countries. The United Kingdom, which was ninth, was the only other Western nation to make the top ten.
Despite the Twitter statistics, the United States actually has relatively few people actually leaving the country to join up. Out of Western nations, Belgium has the highest per capita rate of fighters joining ISIS, whereas France has the highest total number.
The number of fighters joining from Saudi Arabia is between 2,000-2,500, the largest total number, according to the International Centre for the Study of Radicalisation and Political Violence. Per capita, that represents 107 fighters per million people. On a per capita basis, Jordan tops the list, with an estimated 315 fighters per million people.
Belgium has the highest number of fighters per capita of any Western nation. Abdelhamid Abaaoud, a Belgian-born senior Islamic State operative, was suspected to be the key mastermind behind the coordinated attacks on Paris in November. He was killed in a raid at an apartment building in a Paris suburb six days following the attacks.
France is the biggest source of fighters in Europe, contributing 1,200, or 18 per capita. Government figures have put the number of fighters closer to 1,600.
The U.S. is very low on this list — only about 100 fighters have come from the U.S.