The influence of Michael Collins and the pre-Irish Civil War IRA on post-1920s guerrilla campaigns is low and reached its peak in the late 1940s. Yitzhak Shamir, the leader of the Stern gang (or more officially, Lehi) and Vladimir Jabotinsky (who founded Irgun) were both influenced by Michael Collins in their campaigns against the British. However, this made perfect sense for Shamir and Jabotinsky (and, without any solid confirmation, Menachem Begin) since he too was fighting a war of anti-British colonialism. Shamir and Jabotinsky are not the only examples. Subhas Chandra Bose urged his followers to study the IRA. Irish texts were even translated into Burmese during the 1930s and were read by men like Ba Maw.

I've heard plenty of times that Mao Zedong somehow either praised, was influenced by or studied Michael Collins yet I consistently find myself unconvinced that he ever did; there are never any proof provided for it and the academic literature on guerilla warfare never makes a mention of this.

The truth of the matter is that there was never anything really that particularly special or ground breaking about the campaign carried out by Michael Collins. Collins himself was a student of and clearly influenced by the Boer commandos during the Second Boer War (1899-1902) and in particularly of the Boer general Christiaan de Wet, which he based the IRA flying columns on. There are some who claim that he 'invented' urban guerrilla warfare, overlooking the fact that theories had been printed on this since the late 19th century. The main reason for his influence, as we can see above, is that he fought a relatively successful guerrilla war against the British and was involved in anti-British activities. This clearly brought him and his methods to the attention of those also looking to combat the British, but certainly not all of them. It is interesting to note that the guerrilla campaigns during the Irish War of Independence also influenced the creation of the Special Operation Executive during WWII, which is rational since this would have been the most accessible and recent guerrilla warfare campaign to be studied by the British. By the 1950s, his influence appears to have vanished as insurgents the world over looked towards new theories and approaches in the post-war world.

There are many other claims made about Michael Collins as well, in particular as some sort of proto-father of modern guerilla warfare which is very unconvincing in light of how guerrilla warfare became modern in the post-war world. What he truly was, however, was a talented guerrilla leader. There is no doubt about Collin's skills as a commander and the Irish War of Independence is an interesting war to read for anyone interested in early modern guerrilla warfare and counterinsurgency.