Defeating the government of an impoverished, low-tech country in 60 days is not exactly like Napoleon crossing the Alps. It's also not victory.
The US fought for 20 years, could never eliminate the insurgency, and then withdrew with its tail between its legs, leaving the old government to come back to power.
Yes, if you kill 10%, 20%, 30% of the population, maybe you'll eventually destroy the insurgency, though that approach hasn't worked yet for Israel in Gaza. But if you're not completely genocidal, that's not an option.
> This was a lesson the west learned in the world wars
The world wars were not counterinsurgency operations (except from the German and Japanese side in the occupied countries). They were traditional wars between major powers.