Guerrilla warfare is pretty different when not fighting with muskets on a foreign land. Home field advantage and stuff.
The only reason guerrilla warfare worked so well for the revolutionaries is because Britain was dumb enough to travel and fight in straight lines and not move an inch. Took them too long to adjust to actual warfare.
Guerilla warfare was been done forever. The goal of guerilla warfare is just to make it harder for the occupying army to occupy your country and to lower the morale of the occupying army while trying to win the hearts and minds of the people to increase your support. A lot of politics, little fighting.
The us military hasn't fought many enemies who chose asymmetric warfare over conventional warfare, so when the US military went in expecting another WW2/Korea, they got the opposite. You might go to a village, and a woman throws a grenade at you, or your in the jungle and someone a few shots at you, then suddenly they are gone. There were very few moments when the Vietcong chose to fight the western forces head on and each time they did received massive casualties(Tet). Most of the work was also done by the VC through laying bobby traps and harassing people that made contact with Southern Regime and Americans, the NVA didn't do much other than supply the VC who in turn was supplied by the Chinese and USSR.
You also have to remember that warfare also got faster, large caliber bolt action rifles had been replaced by large caliber battle rifles and small caliber assault rifles. Fire fights moved at a quicker paced than those of WW2.
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