A bunch of historical examples can be offered of peoples hiring foreigners to do their fighting for them. The Roman Empire came to rely upon foreigners to fill up the ranks of the army once citizenship became de-linked from soldiering. The Arabs recruited large numbers of Turks driven off the steppe by the Mongols. The little Crusader states in the Holy Land depended upon the military religious orders to aggregate individual European Christian volunteers into formidable props to their survival. The Englishmen John Smith and Guy Fawkes fought for foreign rulers. The French and Spanish armies included regiments of Irish Catholic refugees from English Protestant oppression. In the 19th Century both France and Spain created “Foreign Legions,” while Britain came to prize the Gurkhas. During the Spanish Civil War, the Comintern created the “International Brigades” to fight against the Nationalists. Muslims from many countries fought against the Soviet in Afghanistan. Most recently, the Islamic State marshalled thousands of foreign volunteers under its black flag.
The death of Qassim Suleimani brought some peripheral notice of his reliance upon “foreign legions” to fight as Iranian proxies. Suleimani adroitly used both Shi’ite and—less frequently–Sunni militias on behalf of his government’s long-term effort to expand Iran’s influence in the Middle East. Suleimani deployed these militias in the civil wars in Iraq, Syria, and Yemen, while Hezbollah in Lebanon and Hamas in Gaza are closely linked to Iran. This policy brought so much success that Iran is unlikely to abandon it just because its original architect is dead.
Foreign volunteers have reasons for signing-up. Some come for adventure; some are inspired by religious or ideological commitment; some are veteran soldier seeking something that civilian life can’t provide. The motives for governments that recruit foreign volunteers are less varied. Where military service has become socially undesirable or where the native population possesses skills too great to be wasted on the battlefield, foreign troops allow a country to punch above its weight. Foreign soldiers cost only money. No one cares if they die.
Only about one percent of Americans do military service. Most of those who do serve come from the South and from military families living close to bases scattered through the South and West. Over three-quarters (79 percent) of Army enlistees have a family member who has served in the military; almost a third (30 percent) have a parent who has served. Inevitably, that means that casualties are similarly distributed. This trend has been developing ever since the military became All Volunteer in 1973. There’s a political element to this as well. Politically liberal areas often resist military recruiters in the schools and universities, while liberal parents rarely have done military service. Young people have few models of military service.
Is this one reason for the “forever wars”?
No, I’ve never been a soldier.
 See: https://waroftheworldblog.com/2015/02/24/the-islamic-brigades-1/; https://waroftheworldblog.com/2015/05/08/the-islamic-brigades-ii/; and https://waroftheworldblog.com/2016/06/17/the-islamic-brigades-iii/
 Karim Sadjadpour, “The Sinister Genius of Soleimani,” WSJ, 11-12 January 2020; Dion Nissenbaum and Isabel Coles, “Iraqi Militias Remain a Wild Card,” WSJ, 10 January 2020.
 David Philipps and Tim Arango, “The Call to Serve Is Being Unevenly Embraced,” NYT, 11 January 2020.