>>63908651 (OP)What changed in the 20th century was the politics of guerrillas. (War = extension of politics by other means.) Historically, guerrilas tended to be ideologically conservative, and were more concerned with either kicking out whoever intruded into their mountain valley in extremely inaccesible and marginal places, while otherwise wanting to be left alone, or they were conservative forces resisting some centralizing regime like the War in the Vendee during the French Revolution, but didn't have their goal being the conquest of national power like 20th century guerrillas.
Then in the 20th century you had guerrilla movements begin developing mass popular support. This was part of some cause like poor against the rich, or kicking out the foreigners. The tactics and basic Robin Hood principles were the same (using knowledge of the terrain, mobility, and physical hardiness to outmaneuver and refuse to fight the enemy on his own terms). But the guerrilla's major asset is non-military: he must have the sympathy and support, active and passive, of the local population. Robin Hood without support from the simple villagers is a dead man, and so is any guerrilla. Every textbook of guerrilla warfare begins by pointing this out and make sure to turn on English subtitles here:
https://youtu.be/cZlTKdq4Yb4
Also FYI representing the majority population is an asset. There were numerous examples of failed guerrillas in the 20th century who represented ethnic minorities like communists with their base in the Chinese minority in Malaysia who were defeated by the British.