The other thing to be said about counterinsurgency is that times change, and ideas and technology change with them. During the high tide of Victorian imperialism (also the time of America’s conquest of the Philipines) the gap in military technology between imperialists and the imperialized was enormous. Britain’s colonial service operated on the sensible slogan that “whatever happens we have got / the maxim gun and they have not.” Subjugated peoples had an extremely difficult time acquiring firearms, especially top-notch ones, and ammunition. The weapons of the day broke a lot and were difficult for indigenous peoples to repair or replace. The modern insurgent has recourse to the AK-47, which is cheap as shit, and thanks to modern transportation technology easy to get wherever you’d like. It’s a perfectly good gun, it’s easy to maintain, and you should read all about it in Larry Kahaner’s book.
Obviously, something like the modern American military still has large technological advantages, but they’re much smaller (for these purposes — today’s Air Force could destroy a whole country with nuclear ICMBs if it was ordered to) than the advantages enjoyed by rich countries today. What’s more, literacy is much more widespread and, combined with broadcast media, means you have much deeper and wider levels of political consciousness than you did in the past. Ideas — western ideas, really — about nationalism, self-determination, autonomy, etc. have spread past the point where people are wiling to accept foreign domination.