The US makes much of the fact that foreign fighters are in Iraq. While conceding they are a minority, nevertheless, one hears constant criticism of Syria for allegedly facilitating this phenomenon. We are told that the Syrian border is being swept and patrolled by American and Iraqi forces to prevent entry of coalition forces. Yet in tabulating how many foreign fighters are in Iraq would seem logically to include Americans with roughly 130,000 forces in country. “Iraq in Mesopotamia” which by the way contains many Iraqi partisans does obviously contain foreign fighters whom entered only after the American invasion
From a neutralist perspective, one would have to concede that American intervention far exceeds third-country Arab intervention either by a nation-state or individuals taking up the campaign against the Shi’a and Americans. Also it is essential to understand that American imperialist forces are not welcomed in many parts of the world. Japan is reducing their number in Okinawa. Uzbekistan basically expelled them a year ago by closing a base. Some have been relocated from Korea to Iraq and I predict that South Korea will find it increasingly untenable to maintain roughly 38,000 troops in that country.
During Vietnam the criminal Johnson and Nixon administration would emphasise how South Vietnam was invaded by the North and how this external aggression had to be reversed to prevent the "fall" of the south under Communism. Disregarding this for a moment, Vietnam was primarily a civil war between southerners and not, even though I believe it would have still qualified, as a civil war, primarily between South and North Vietnam. Admittedly, as the US introduced 100,000s more troops beginning in 1965 and ultimately reaching about 543,000 in April 1969, the North would increase their support of the Viet Cong.
Also in civil wars, it is common to have outside support. The US revolution, that could be seen as a civil war from the British perspective, would not have succeeded without French military support such as Yorktown with Admiral de Grasse. So outside Arab assistance, which I am claiming is rather paltry in Iraq in comparison to U.S. involvement, is quite common in civil, revolutionary and other types of conflicts.